diff --git a/bindings/tpython/src/TPyClassGenerator.cxx b/bindings/tpython/src/TPyClassGenerator.cxx
index a1dd348ff50f6..5bcc6605ee652 100644
--- a/bindings/tpython/src/TPyClassGenerator.cxx
+++ b/bindings/tpython/src/TPyClassGenerator.cxx
@@ -22,6 +22,7 @@
 #include "TClass.h"
 #include "TInterpreter.h"
 #include "TROOT.h"
+#include "TList.h"
 
 // Standard
 #include <sstream>
diff --git a/core/base/inc/Rtypes.h b/core/base/inc/Rtypes.h
index 1c6c7a701162b..547a596fab883 100644
--- a/core/base/inc/Rtypes.h
+++ b/core/base/inc/Rtypes.h
@@ -21,7 +21,7 @@
 
 
 #include "RtypesCore.h"
-#include "DllImport.h"
+// #include "DllImport.h" // included via RtypesCore.h, not used here
 
 #include "snprintf.h"   // part of stdio.h on systems that have it
 #include "strlcpy.h"    // part of string.h on systems that have it
diff --git a/core/base/inc/TColor.h b/core/base/inc/TColor.h
index 00dae58b8fac2..17ab90276919e 100644
--- a/core/base/inc/TColor.h
+++ b/core/base/inc/TColor.h
@@ -13,8 +13,8 @@
 #define ROOT_TColor
 
 #include "TNamed.h"
-#include "TArrayI.h"
 
+class TArrayI;
 
 class TColor : public TNamed {
 protected:
diff --git a/core/base/inc/TFileInfo.h b/core/base/inc/TFileInfo.h
index e38046d5b74c6..3dd9c1aa7c74e 100644
--- a/core/base/inc/TFileInfo.h
+++ b/core/base/inc/TFileInfo.h
@@ -21,14 +21,17 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TNamed.h"
+#include "TList.h"
 
+#ifdef R__LESS_INCLUDES
+class TUrl;
+class TUUID;
+class TMD5;
+#else
 #include "TUrl.h"
-
 #include "TUUID.h"
-
 #include "TMD5.h"
-
-#include "TList.h"
+#endif
 
 class TFileInfoMeta;
 
diff --git a/core/base/inc/TObject.h b/core/base/inc/TObject.h
index 58c09609f6989..32853ef710e74 100644
--- a/core/base/inc/TObject.h
+++ b/core/base/inc/TObject.h
@@ -13,7 +13,7 @@
 #define ROOT_TObject
 
 
-#include "RConfigure.h"
+// #include "RConfigure.h"  // included via Rtypes.h
 #include "Rtypes.h"
 #include "TStorage.h"
 #include "TVersionCheck.h"
diff --git a/core/base/inc/TParameter.h b/core/base/inc/TParameter.h
index fb8900a9bfb8e..f136f62f8a69f 100644
--- a/core/base/inc/TParameter.h
+++ b/core/base/inc/TParameter.h
@@ -23,8 +23,6 @@
 
 #include "Riostream.h"
 
-#include "TClass.h"
-
 #include "TObject.h"
 
 #include "TCollection.h"
diff --git a/core/base/inc/TPluginManager.h b/core/base/inc/TPluginManager.h
index 084657069abc6..ec58c1420253e 100644
--- a/core/base/inc/TPluginManager.h
+++ b/core/base/inc/TPluginManager.h
@@ -94,7 +94,6 @@ class TEnv;
 class TList;
 class THashTable;
 class TFunction;
-class TMethodCall;
 class TPluginManager;
 
 #include <atomic>
diff --git a/core/base/inc/TProcessID.h b/core/base/inc/TProcessID.h
index 1331b48a03c57..7d48454e387b1 100644
--- a/core/base/inc/TProcessID.h
+++ b/core/base/inc/TProcessID.h
@@ -23,7 +23,12 @@
 
 
 #include "TNamed.h"
+
+#ifdef R__LESS_INCLUDES
+class TObjArray;
+#else
 #include "TObjArray.h"
+#endif
 
 #include <atomic>
 #include <type_traits>
diff --git a/core/base/inc/TROOT.h b/core/base/inc/TROOT.h
index dcbb93ee72f3c..dce79c0330d1f 100644
--- a/core/base/inc/TROOT.h
+++ b/core/base/inc/TROOT.h
@@ -26,8 +26,8 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TDirectory.h"
-#include "TList.h"
-#include "RConfigure.h"
+// #include "TList.h"  // included in TDirectory.h
+// #include "RConfigure.h"  // included via Rtypes.h
 
 #include <atomic>
 #include <string>
@@ -55,6 +55,7 @@ class TListOfDataMembers;
 class TListOfEnums;
 class TListOfFunctions;
 class TListOfFunctionTemplates;
+class TSeqCollection;
 class TFunctionTemplate;
 class TGlobalMappedFunction;
 
@@ -270,8 +271,8 @@ friend TROOT *ROOT::Internal::GetROOT2();
    TObject          *GetGeometry(const char *name) const;
    const TObject    *GetSelectedPrimitive() const { return fPrimitive; }
    TVirtualPad      *GetSelectedPad() const { return fSelectPad; }
-   Int_t             GetNclasses() const { return fClasses->GetSize(); }
-   Int_t             GetNtypes() const { return fTypes->GetSize(); }
+   Int_t             GetNclasses() const;
+   Int_t             GetNtypes() const;
    TFolder          *GetRootFolder() const { return fRootFolder; }
    TProcessUUID     *GetUUIDs() const { return fUUIDs; }
    const TString    &GetWebDisplay() const { return fWebDisplay; }
diff --git a/core/base/inc/TStorage.h b/core/base/inc/TStorage.h
index c45ee031a5d1d..8967dc6220848 100644
--- a/core/base/inc/TStorage.h
+++ b/core/base/inc/TStorage.h
@@ -21,7 +21,7 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "RConfigure.h"
+// #include "RConfigure.h" // included via Rtypes.h
 #include "Rtypes.h"
 
 typedef void (*FreeHookFun_t)(void*, void *addr, size_t);
diff --git a/core/base/inc/TStyle.h b/core/base/inc/TStyle.h
index c8370a3e19558..0a747f0604bce 100644
--- a/core/base/inc/TStyle.h
+++ b/core/base/inc/TStyle.h
@@ -12,16 +12,18 @@
 #ifndef ROOT_TStyle
 #define ROOT_TStyle
 
-
 #include "TNamed.h"
-#include "TAttAxis.h"
 #include "TAttLine.h"
 #include "TAttFill.h"
-#include "TAttText.h"
 #include "TAttMarker.h"
-#include "TArrayI.h"
+#include "TAttText.h"
+#include "TAttAxis.h"
 #include "TColor.h"
 
+#ifndef R__LESS_INCLUDES
+#include "TArrayI.h"
+#endif
+
 class TBrowser;
 
 class TStyle : public TNamed, public TAttLine, public TAttFill, public TAttMarker, public TAttText {
diff --git a/core/base/inc/TTask.h b/core/base/inc/TTask.h
index 910bc960a057a..2d9aa60edca81 100644
--- a/core/base/inc/TTask.h
+++ b/core/base/inc/TTask.h
@@ -22,7 +22,12 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TNamed.h"
+
+#ifdef R__LESS_INCLUDES
+class TList;
+#else
 #include "TList.h"
+#endif
 
 class TBrowser;
 
@@ -50,7 +55,7 @@ class TTask : public TNamed {
    TTask& operator=(const TTask& tt);
 
    virtual void  Abort();  // *MENU*
-   virtual void  Add(TTask *task) {fTasks->Add(task);}
+   virtual void  Add(TTask *task);
    virtual void  Browse(TBrowser *b);
    virtual void  CleanTasks();
    virtual void  Clear(Option_t *option="");
diff --git a/core/base/inc/TUrl.h b/core/base/inc/TUrl.h
index f5d11911d1f5a..20edb4f624762 100644
--- a/core/base/inc/TUrl.h
+++ b/core/base/inc/TUrl.h
@@ -26,8 +26,6 @@
 
 #include "TObject.h"
 #include "TString.h"
-#include "TMap.h"
-
 
 class THashList;
 class TMap;
diff --git a/core/base/inc/TVirtualMonitoring.h b/core/base/inc/TVirtualMonitoring.h
index a779f336f6536..8d33c03412b1c 100644
--- a/core/base/inc/TVirtualMonitoring.h
+++ b/core/base/inc/TVirtualMonitoring.h
@@ -22,8 +22,13 @@
 
 #include "TNamed.h"
 
+#ifdef R__LESS_INCLUDES
+class TList;
+class TMap;
+#else
 #include "TList.h"
 #include "TMap.h"
+#endif
 
 class TFile;
 
@@ -31,8 +36,8 @@ class TVirtualMonitoringWriter : public TNamed {
 
 private:
 
-   TVirtualMonitoringWriter(const TVirtualMonitoringWriter&); // Not implemented
-   TVirtualMonitoringWriter& operator=(const TVirtualMonitoringWriter&); // Not implemented
+   TVirtualMonitoringWriter(const TVirtualMonitoringWriter&) = delete;
+   TVirtualMonitoringWriter& operator=(const TVirtualMonitoringWriter&) = delete;
 
    Double_t fValue;  // double monitor value
 
@@ -44,7 +49,7 @@ class TVirtualMonitoringWriter : public TNamed {
    TVirtualMonitoringWriter(const char *name, Double_t value)
      : TNamed(name, ""), fValue(value), fTmpOpenPhases(0) { }
 
-   virtual ~TVirtualMonitoringWriter() { if (fTmpOpenPhases) delete fTmpOpenPhases; }
+   virtual ~TVirtualMonitoringWriter();
 
    // TFile related info. In general they are gathered and sent only sometimes as summaries
    virtual Bool_t SendFileCloseEvent(TFile * /*file*/)
diff --git a/core/base/inc/TVirtualMutex.h b/core/base/inc/TVirtualMutex.h
index c06f12e6872c5..94a44493e6412 100644
--- a/core/base/inc/TVirtualMutex.h
+++ b/core/base/inc/TVirtualMutex.h
@@ -24,8 +24,6 @@
 
 #include "TObject.h"
 
-#include <memory>
-
 class TVirtualMutex;
 
 // Global mutex set in TThread::Init
diff --git a/core/base/inc/TVirtualRWMutex.h b/core/base/inc/TVirtualRWMutex.h
index 03d98ead2ac17..9a998289cd6b1 100644
--- a/core/base/inc/TVirtualRWMutex.h
+++ b/core/base/inc/TVirtualRWMutex.h
@@ -25,6 +25,7 @@
 
 #include "TVirtualMutex.h"
 
+#include <memory>
 
 namespace ROOT {
 
diff --git a/core/base/inc/TVirtualViewer3D.h b/core/base/inc/TVirtualViewer3D.h
index 2b68dfe9e52e0..6fd4882092bfe 100644
--- a/core/base/inc/TVirtualViewer3D.h
+++ b/core/base/inc/TVirtualViewer3D.h
@@ -24,12 +24,8 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "Rtypes.h"
-
 #include "TObject.h"
 
-#include "TAttFill.h"
-
 class TBuffer3D;
 class TVirtualPad;
 class TGLRect;
diff --git a/core/base/src/TFileCollection.cxx b/core/base/src/TFileCollection.cxx
index 295f06f06d9dc..ae04d0298d845 100644
--- a/core/base/src/TFileCollection.cxx
+++ b/core/base/src/TFileCollection.cxx
@@ -26,6 +26,8 @@ collection of TFile names.
 #include "TObjString.h"
 #include "TUri.h"
 #include "TUrl.h"
+#include "TUUID.h"
+#include "TMD5.h"
 #include "TSystem.h"
 #include "Riostream.h"
 #include "TRegexp.h"
diff --git a/core/base/src/TFileInfo.cxx b/core/base/src/TFileInfo.cxx
index 58329d4b18fd0..6c7e7113e2428 100644
--- a/core/base/src/TFileInfo.cxx
+++ b/core/base/src/TFileInfo.cxx
@@ -20,7 +20,9 @@ Class describing a generic file including meta information.
 #include "TRegexp.h"
 #include "TSystem.h"
 #include "TClass.h"
-
+#include "TUrl.h"
+#include "TUUID.h"
+#include "TMD5.h"
 
 ClassImp(TFileInfo);
 ClassImp(TFileInfoMeta);
diff --git a/core/base/src/TFolder.cxx b/core/base/src/TFolder.cxx
index 1d506b3431242..ac7fa1a8ab089 100644
--- a/core/base/src/TFolder.cxx
+++ b/core/base/src/TFolder.cxx
@@ -86,6 +86,7 @@ if this pointer is used frequently or inside loops.
 #include "Strlen.h"
 #include "TFolder.h"
 #include "TBrowser.h"
+#include "TList.h"
 #include "TROOT.h"
 #include "TClass.h"
 #include "TError.h"
diff --git a/core/base/src/TPluginManager.cxx b/core/base/src/TPluginManager.cxx
index 31fbd0cf523a9..1f654c62d70ea 100644
--- a/core/base/src/TPluginManager.cxx
+++ b/core/base/src/TPluginManager.cxx
@@ -79,7 +79,6 @@ TFile, TSQLServer, TGrid, etc. functionality.
 */
 
 #include "TPluginManager.h"
-#include "Varargs.h"
 #include "TEnv.h"
 #include "TRegexp.h"
 #include "TROOT.h"
diff --git a/core/base/src/TProcessUUID.cxx b/core/base/src/TProcessUUID.cxx
index 5d7626a633555..ad21cf2d9abbf 100644
--- a/core/base/src/TProcessUUID.cxx
+++ b/core/base/src/TProcessUUID.cxx
@@ -41,11 +41,11 @@ TProcessID *fPID in TRef points to the unique object TProcessUUID.
 The TRef uniqueID is directly the UUIDNumber=slot number.
 */
 
-#include "TROOT.h"
 #include "TProcessUUID.h"
 #include "THashList.h"
 #include "TBits.h"
 #include "TObjString.h"
+#include "TObjArray.h"
 #include "TUUID.h"
 
 ClassImp(TProcessUUID);
diff --git a/core/base/src/TQCommand.cxx b/core/base/src/TQCommand.cxx
index 590fa0e917dd6..0791937a7661e 100644
--- a/core/base/src/TQCommand.cxx
+++ b/core/base/src/TQCommand.cxx
@@ -101,7 +101,6 @@ Use TQUndoManager::Undo to undo commands in  history list.
 Redo is Undo for undo action. Use TQUndoManager::Redo method for that
 */
 
-#include "Varargs.h"
 #include "TQCommand.h"
 #include "TQConnection.h"
 #include "TDataType.h"
diff --git a/core/base/src/TQConnection.cxx b/core/base/src/TQConnection.cxx
index e4e8e3ada39d9..746ec60b35737 100644
--- a/core/base/src/TQConnection.cxx
+++ b/core/base/src/TQConnection.cxx
@@ -21,7 +21,6 @@ communication mechanism.
    -  receiver is the object to which slot-method is applied
 */
 
-#include "Varargs.h"
 #include "TQConnection.h"
 #include "TROOT.h"
 #include "TRefCnt.h"
diff --git a/core/base/src/TQObject.cxx b/core/base/src/TQObject.cxx
index ef9cdb90ac03c..ed1a0ef887a1b 100644
--- a/core/base/src/TQObject.cxx
+++ b/core/base/src/TQObject.cxx
@@ -52,7 +52,6 @@ as an identifier of the modifier method.
 General purpose message signal
 */
 
-#include "Varargs.h"
 #include "TQObject.h"
 #include "TQConnection.h"
 #include "THashList.h"
diff --git a/core/base/src/TROOT.cxx b/core/base/src/TROOT.cxx
index f0d8dbff2edc5..f32b4b1abfa28 100644
--- a/core/base/src/TROOT.cxx
+++ b/core/base/src/TROOT.cxx
@@ -1802,6 +1802,21 @@ TCollection *TROOT::GetListOfTypes(Bool_t /* load */)
    return fTypes;
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Get number of classes.
+
+Int_t TROOT::GetNclasses() const
+{
+   return fClasses->GetSize();
+}
+
+////////////////////////////////////////////////////////////////////////////////
+/// Get number of types.
+
+Int_t TROOT::GetNtypes() const
+{
+   return fTypes->GetSize();
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 /// Execute command when system has been idle for idleTimeInSec seconds.
diff --git a/core/base/src/TTask.cxx b/core/base/src/TTask.cxx
index 908519ce24397..99b03f4230628 100644
--- a/core/base/src/TTask.cxx
+++ b/core/base/src/TTask.cxx
@@ -81,6 +81,7 @@ the following script:
 #include "Riostream.h"
 #include "TTask.h"
 #include "TBrowser.h"
+#include "TList.h"
 #include "TROOT.h"
 #include "TRegexp.h"
 
@@ -164,6 +165,16 @@ TTask::~TTask()
    delete fTasks;
 }
 
+
+////////////////////////////////////////////////////////////////////////////////
+/// Add TTask to this.
+
+void  TTask::Add(TTask *task) 
+{
+   fTasks->Add(task);
+}
+
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Abort current tree of tasks.
 /// After this call, the tree of tasks is ready to be executed again.
diff --git a/core/base/src/TVirtualMonitoring.cxx b/core/base/src/TVirtualMonitoring.cxx
index a4f130c1fc48e..cb40412bf8eb8 100644
--- a/core/base/src/TVirtualMonitoring.cxx
+++ b/core/base/src/TVirtualMonitoring.cxx
@@ -18,6 +18,7 @@ Provides the interface for externel Monitoring
 
 #include "TVirtualMonitoring.h"
 
+#include "TList.h"
 
 ClassImp(TVirtualMonitoringWriter);
 ClassImp(TVirtualMonitoringReader);
@@ -26,3 +27,11 @@ ClassImp(TVirtualMonitoringReader);
 TVirtualMonitoringWriter *gMonitoringWriter = 0;
 TVirtualMonitoringReader *gMonitoringReader = 0;
 
+////////////////////////////////////////////////////////////
+/// destructor
+
+TVirtualMonitoringWriter::~TVirtualMonitoringWriter() 
+{
+   if (fTmpOpenPhases) 
+      delete fTmpOpenPhases; 
+}
diff --git a/core/cont/inc/TArray.h b/core/cont/inc/TArray.h
index 1cb5041ef1e8e..42f29d6f27668 100644
--- a/core/cont/inc/TArray.h
+++ b/core/cont/inc/TArray.h
@@ -24,7 +24,6 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "Rtypes.h"
-#include <string.h>
 
 class TBuffer;
 
diff --git a/core/cont/inc/TBits.h b/core/cont/inc/TBits.h
index a89d0fe959bbb..5b3e17470b64b 100644
--- a/core/cont/inc/TBits.h
+++ b/core/cont/inc/TBits.h
@@ -20,7 +20,6 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "Rtypes.h"
 #include "TObject.h"
 #include <string.h>
 
diff --git a/core/cont/inc/TClonesArray.h b/core/cont/inc/TClonesArray.h
index 50232683d18f2..c23e90f54e729 100644
--- a/core/cont/inc/TClonesArray.h
+++ b/core/cont/inc/TClonesArray.h
@@ -22,13 +22,10 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "Rtypes.h"
-
 #include "TObjArray.h"
 
 class TClass;
 
-
 class TClonesArray : public TObjArray {
 
 protected:
diff --git a/core/cont/src/TClassTable.cxx b/core/cont/src/TClassTable.cxx
index 72a55b2e1fa5a..cabfbc193eb13 100644
--- a/core/cont/src/TClassTable.cxx
+++ b/core/cont/src/TClassTable.cxx
@@ -22,6 +22,7 @@ initialized when the program starts (see the ClassImp macro).
 #include "TClass.h"
 #include "TClassEdit.h"
 #include "TProtoClass.h"
+#include "TList.h"
 #include "TROOT.h"
 #include "TString.h"
 #include "TError.h"
diff --git a/core/cont/src/TObjectTable.cxx b/core/cont/src/TObjectTable.cxx
index d5c348ac4befa..85ae62eaa0020 100644
--- a/core/cont/src/TObjectTable.cxx
+++ b/core/cont/src/TObjectTable.cxx
@@ -82,6 +82,7 @@ via the command gObjectTable->Print()
 */
 
 #include "TObjectTable.h"
+#include "TList.h"
 #include "TROOT.h"
 #include "TClass.h"
 #include "TError.h"
diff --git a/core/gui/inc/TContextMenu.h b/core/gui/inc/TContextMenu.h
index 89f2d0154bf7b..8573eaf130fdc 100644
--- a/core/gui/inc/TContextMenu.h
+++ b/core/gui/inc/TContextMenu.h
@@ -23,10 +23,14 @@
 //                                                                            //
 ////////////////////////////////////////////////////////////////////////////////
 
-#include "TContextMenuImp.h"
-
 #include "TNamed.h"
 
+#ifdef R__LESS_INCLUDES
+class TContextMenuImp;
+#else
+#include "TContextMenuImp.h"
+#endif
+
 class TMethod;
 class TFunction;
 class TMethodArg;
@@ -55,8 +59,7 @@ friend class  TContextMenuImp;
    TVirtualPad     *fSelectedPad;         //selected pad (if exist)
    TBrowser        *fBrowser;             //selected browser (if exist)
 
-   virtual void DisplayPopUp(Int_t x, Int_t y)
-      { if (fContextMenuImp) fContextMenuImp->DisplayPopup(x, y); }
+   virtual void DisplayPopUp(Int_t x, Int_t y);
 
 private:
    TContextMenu();
diff --git a/core/gui/inc/TToggle.h b/core/gui/inc/TToggle.h
index 96e5ceebe7f31..891138cb567c5 100644
--- a/core/gui/inc/TToggle.h
+++ b/core/gui/inc/TToggle.h
@@ -34,11 +34,15 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TObject.h"
-#include "TMethodCall.h"
-#include "TMethod.h"
 #include "TNamed.h"
 
+#ifdef R__LESS_INCLUDES
+class TMethodCall;
+class TMethod;
+#else
+#include "TMethodCall.h"
+#include "TMethod.h"
+#endif
 
 class TToggle: public TNamed {
 
diff --git a/core/gui/src/TContextMenu.cxx b/core/gui/src/TContextMenu.cxx
index f31240072e933..b07f690828906 100644
--- a/core/gui/src/TContextMenu.cxx
+++ b/core/gui/src/TContextMenu.cxx
@@ -37,6 +37,7 @@ The picture below shows a canvas with a pop-up menu and a dialog box.
 
 #include "TROOT.h"
 #include "TContextMenu.h"
+#include "TContextMenuImp.h"
 #include "TVirtualPad.h"
 #include "TGuiFactory.h"
 #include "TMethod.h"
@@ -303,6 +304,16 @@ const char *TContextMenu::CreatePopupTitle(TObject *object)
    return popupTitle.Data();
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Display popup.
+
+void TContextMenu::DisplayPopUp(Int_t x, Int_t y)
+{
+   if (fContextMenuImp)
+      fContextMenuImp->DisplayPopup(x, y);
+}
+
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Execute method with specified arguments for specified object.
 
diff --git a/core/gui/src/TObjectSpy.cxx b/core/gui/src/TObjectSpy.cxx
index 63cbfadf3de5b..454ce481dad3e 100644
--- a/core/gui/src/TObjectSpy.cxx
+++ b/core/gui/src/TObjectSpy.cxx
@@ -10,6 +10,7 @@
  *************************************************************************/
 
 #include "TObjectSpy.h"
+#include "TSeqCollection.h"
 #include "TROOT.h"
 #include "TVirtualMutex.h"
 
diff --git a/core/gui/src/TToggle.cxx b/core/gui/src/TToggle.cxx
index e91d9f459bd30..02927efbcf47d 100644
--- a/core/gui/src/TToggle.cxx
+++ b/core/gui/src/TToggle.cxx
@@ -28,6 +28,7 @@ with name GetXXX, IsXXX or HasXXX for given object.
 */
 
 #include "TMethod.h"
+#include "TMethodCall.h"
 #include "TToggle.h"
 #include "TDataMember.h"
 
diff --git a/core/imt/inc/ROOT/TThreadExecutor.hxx b/core/imt/inc/ROOT/TThreadExecutor.hxx
index d07a0e84f7094..e4047c4c18d79 100644
--- a/core/imt/inc/ROOT/TThreadExecutor.hxx
+++ b/core/imt/inc/ROOT/TThreadExecutor.hxx
@@ -24,7 +24,6 @@
 
 #include "ROOT/TExecutor.hxx"
 #include "ROOT/TPoolManager.hxx"
-#include "TROOT.h"
 #include "TError.h"
 #include <functional>
 #include <memory>
diff --git a/core/imt/src/TThreadExecutor.cxx b/core/imt/src/TThreadExecutor.cxx
index c2e3e0993773d..e6b7d9380bd6c 100644
--- a/core/imt/src/TThreadExecutor.cxx
+++ b/core/imt/src/TThreadExecutor.cxx
@@ -1,6 +1,8 @@
 #include "ROOT/TThreadExecutor.hxx"
 #include "ROOT/TTaskGroup.hxx"
 
+#include "TROOT.h"
+
 #if !defined(_MSC_VER)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wshadow"
diff --git a/core/meta/inc/TClassStreamer.h b/core/meta/inc/TClassStreamer.h
index 4cca4e1d612e5..5170eceadc41f 100644
--- a/core/meta/inc/TClassStreamer.h
+++ b/core/meta/inc/TClassStreamer.h
@@ -12,7 +12,6 @@
 #ifndef ROOT_TClassStreamer_h
 #define ROOT_TClassStreamer_h
 
-#include "Rtypes.h"
 #include "TClassRef.h"
 
 //////////////////////////////////////////////////////////////////////////
diff --git a/core/meta/inc/TGenericClassInfo.h b/core/meta/inc/TGenericClassInfo.h
index 9867e347f9ef4..14a0a6e83b231 100644
--- a/core/meta/inc/TGenericClassInfo.h
+++ b/core/meta/inc/TGenericClassInfo.h
@@ -12,9 +12,9 @@
 #ifndef ROOT_TGenericClassInfo
 #define ROOT_TGenericClassInfo
 
-#include <vector>
-#include "TSchemaHelper.h"
 #include "Rtypes.h"
+#include "TSchemaHelper.h"
+#include <vector>
 
 // Forward declarations
 class TVirtualIsAProxy;
diff --git a/core/meta/inc/TMemberStreamer.h b/core/meta/inc/TMemberStreamer.h
index 9ed02c478d757..d6919b8040881 100644
--- a/core/meta/inc/TMemberStreamer.h
+++ b/core/meta/inc/TMemberStreamer.h
@@ -12,7 +12,6 @@
 #ifndef ROOT_TMemberStreamer
 #define ROOT_TMemberStreamer
 
-#include "Rtypes.h"
 #include "TClassRef.h"
 
 //////////////////////////////////////////////////////////////////////////
diff --git a/core/meta/inc/TMethodArg.h b/core/meta/inc/TMethodArg.h
index 348a89178d994..75b7913cf1623 100644
--- a/core/meta/inc/TMethodArg.h
+++ b/core/meta/inc/TMethodArg.h
@@ -23,7 +23,11 @@
 
 #include "TDictionary.h"
 
+#ifdef R__LESS_INCLUDES
+class TDataMember;
+#else
 #include "TDataMember.h"
+#endif
 
 class TFunction;
 class TMethod;
diff --git a/core/meta/inc/TMethodCall.h b/core/meta/inc/TMethodCall.h
index 578d4c9ffe959..b5aa8c6c4e90d 100644
--- a/core/meta/inc/TMethodCall.h
+++ b/core/meta/inc/TMethodCall.h
@@ -27,7 +27,7 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TDictionary.h"
+#include "TObject.h"
 
 #include "TInterpreter.h"
 
diff --git a/core/meta/inc/TProtoClass.h b/core/meta/inc/TProtoClass.h
index 84c65b53d3e6b..10643da55ffb0 100644
--- a/core/meta/inc/TProtoClass.h
+++ b/core/meta/inc/TProtoClass.h
@@ -15,13 +15,16 @@
 
 #include "TNamed.h"
 
+#include <vector>
+
 class TClass;
 class TList;
 class TRealData;
-
+#ifdef R__LESS_INCLUDES
+class TDataMember;
+#else
 #include "TDataMember.h"
-
-#include <vector>
+#endif
 
 //////////////////////////////////////////////////////////////////////////
 //                                                                      //
diff --git a/core/meta/inc/TSchemaRule.h b/core/meta/inc/TSchemaRule.h
index 176f8d7de0352..f5265b7f394f9 100644
--- a/core/meta/inc/TSchemaRule.h
+++ b/core/meta/inc/TSchemaRule.h
@@ -4,18 +4,16 @@
 #ifndef ROOT_TSchemaRule
 #define ROOT_TSchemaRule
 
-class TBuffer;
-class TVirtualObject;
-class TObjArray;
-
-#include "TObject.h"
 #include "TNamed.h"
-#include "Rtypes.h"
 #include "TString.h"
 
 #include <vector>
 #include <utility>
 
+class TBuffer;
+class TVirtualObject;
+class TObjArray;
+
 namespace ROOT {
 
    class TSchemaRule: public TObject
diff --git a/core/meta/inc/TSchemaRuleSet.h b/core/meta/inc/TSchemaRuleSet.h
index 961c70aec03e5..609e0c0d3506a 100644
--- a/core/meta/inc/TSchemaRuleSet.h
+++ b/core/meta/inc/TSchemaRuleSet.h
@@ -4,14 +4,17 @@
 #ifndef ROOT_TSchemaRuleSet
 #define ROOT_TSchemaRuleSet
 
-class TClass;
-
 #include "TObject.h"
-#include "TObjArray.h"
-#include "Rtypes.h"
 #include "TString.h"
 #include "TClassRef.h"
 
+#ifdef R__LESS_INCLUDES
+class TObjArray;
+#else
+#include "TObjArray.h"
+#endif
+
+
 namespace ROOT {
 
 class TSchemaRule;
diff --git a/core/meta/inc/TStatusBitsChecker.h b/core/meta/inc/TStatusBitsChecker.h
index 1d655216bac56..5a2ff6d36c249 100644
--- a/core/meta/inc/TStatusBitsChecker.h
+++ b/core/meta/inc/TStatusBitsChecker.h
@@ -12,7 +12,6 @@
 #ifndef ROOT_TStatusBitsChecker
 #define ROOT_TStatusBitsChecker
 
-#include <string>
 #include <map>
 #include <list>
 
diff --git a/core/meta/src/TCheckHashRecursiveRemoveConsistency.h b/core/meta/src/TCheckHashRecursiveRemoveConsistency.h
index 3eaac2072ab9a..17fc7be9464fc 100644
--- a/core/meta/src/TCheckHashRecursiveRemoveConsistency.h
+++ b/core/meta/src/TCheckHashRecursiveRemoveConsistency.h
@@ -16,7 +16,6 @@
 #include "TClass.h"
 #include "TError.h"
 #include "TMethod.h"
-#include "TROOT.h"
 
 #include <list>
 
diff --git a/core/meta/src/TFunction.cxx b/core/meta/src/TFunction.cxx
index c742511b61012..00e9b2046f916 100644
--- a/core/meta/src/TFunction.cxx
+++ b/core/meta/src/TFunction.cxx
@@ -18,6 +18,7 @@ functions (accessible via TROOT::GetListOfGlobalFunctions()).
 
 #include "TFunction.h"
 #include "TMethodArg.h"
+#include "TList.h"
 #include "TROOT.h"
 #include "TInterpreter.h"
 #include "Strlen.h"
diff --git a/core/meta/src/TStreamerElement.cxx b/core/meta/src/TStreamerElement.cxx
index e2d4a66ef0d3c..c1eb2ac79a431 100644
--- a/core/meta/src/TStreamerElement.cxx
+++ b/core/meta/src/TStreamerElement.cxx
@@ -28,6 +28,7 @@
 #include "TDataType.h"
 #include "TRealData.h"
 #include "ThreadLocalStorage.h"
+#include "TList.h"
 #include "TRef.h"
 #include "TInterpreter.h"
 #include "TError.h"
diff --git a/core/rint/src/TTabCom.cxx b/core/rint/src/TTabCom.cxx
index 35224293ac21e..478fb7a1c5bef 100644
--- a/core/rint/src/TTabCom.cxx
+++ b/core/rint/src/TTabCom.cxx
@@ -129,6 +129,7 @@
 #include "TTabCom.h"
 #include "TClass.h"
 #include "TClassTable.h"
+#include "TDataMember.h"
 #include "TSystem.h"
 #include "TROOT.h"
 #include "TMethod.h"
diff --git a/core/thread/inc/TConditionImp.h b/core/thread/inc/TConditionImp.h
index 4caa39eca74e7..fdd22b2e10fb3 100644
--- a/core/thread/inc/TConditionImp.h
+++ b/core/thread/inc/TConditionImp.h
@@ -12,7 +12,6 @@
 #ifndef ROOT_TConditionImp
 #define ROOT_TConditionImp
 
-
 //////////////////////////////////////////////////////////////////////////
 //                                                                      //
 // TConditionImp                                                        //
@@ -22,10 +21,8 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "Rtypes.h"
 #include "TObject.h"
 
-
 class TConditionImp : public TObject {
 
 public:
diff --git a/core/thread/inc/TMutexImp.h b/core/thread/inc/TMutexImp.h
index c0ca36be3fdc6..f7eb10ece9b70 100644
--- a/core/thread/inc/TMutexImp.h
+++ b/core/thread/inc/TMutexImp.h
@@ -22,11 +22,8 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "Rtypes.h"
 #include "TObject.h"
 
-#include "TVirtualMutex.h"
-
 class TMutexImp : public TObject {
 
 public:
diff --git a/core/thread/inc/TThread.h b/core/thread/inc/TThread.h
index 26fb49f47aca0..3664c4d110440 100644
--- a/core/thread/inc/TThread.h
+++ b/core/thread/inc/TThread.h
@@ -24,15 +24,19 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TObject.h"
-#include "TCondition.h"
+#include "TNamed.h"
 #include "TTimer.h"
-#include "Varargs.h"
+#include <stdarg.h>
+
+#ifdef R__LESS_INCLUDES
+class TCondition;
+#else
+#include "TCondition.h"
+#endif
 
 class TMutex;
 class TThreadImp;
 
-
 class TThread : public TNamed {
 
 friend class TThreadImp;
diff --git a/core/thread/inc/TThreadImp.h b/core/thread/inc/TThreadImp.h
index cbe353a392607..8bcd272778c70 100644
--- a/core/thread/inc/TThreadImp.h
+++ b/core/thread/inc/TThreadImp.h
@@ -25,7 +25,8 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TObject.h"
-#include "TThread.h"
+
+class TThread;
 
 class TThreadImp : public TObject {
 public:
diff --git a/core/thread/src/TPosixThread.cxx b/core/thread/src/TPosixThread.cxx
index 0a4c65d5c7c42..bd4decfed7b14 100644
--- a/core/thread/src/TPosixThread.cxx
+++ b/core/thread/src/TPosixThread.cxx
@@ -19,6 +19,7 @@
 
 #include "TPosixThread.h"
 
+#include "TThread.h"
 
 ClassImp(TPosixThread);
 
diff --git a/core/thread/src/TThread.cxx b/core/thread/src/TThread.cxx
index 63f711f69c19a..0410e3814e342 100644
--- a/core/thread/src/TThread.cxx
+++ b/core/thread/src/TThread.cxx
@@ -26,6 +26,7 @@
 #include "TThreadImp.h"
 #include "TThreadFactory.h"
 #include "TROOT.h"
+#include "TCondition.h"
 #include "TApplication.h"
 #include "TVirtualPad.h"
 #include "TMethodCall.h"
diff --git a/core/thread/src/TWin32Thread.cxx b/core/thread/src/TWin32Thread.cxx
index a0ce0ed64575a..9f2b021ac8879 100644
--- a/core/thread/src/TWin32Thread.cxx
+++ b/core/thread/src/TWin32Thread.cxx
@@ -18,6 +18,9 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TWin32Thread.h"
+
+#include "TThread.h"
+
 #include <process.h>
 #include <errno.h>
 
diff --git a/geom/gdml/inc/TGDMLParse.h b/geom/gdml/inc/TGDMLParse.h
index 9de8e9926706e..9696af6078f00 100644
--- a/geom/gdml/inc/TGDMLParse.h
+++ b/geom/gdml/inc/TGDMLParse.h
@@ -16,6 +16,7 @@
 #include "TXMLEngine.h"
 #include "TGeoMatrix.h"
 #include "TGeoVolume.h"
+#include "TGeoElement.h"
 
 #include <map>
 #include <iostream>
diff --git a/geom/gdml/inc/TGDMLWrite.h b/geom/gdml/inc/TGDMLWrite.h
index 6ab548de23229..42e594b5af9d8 100644
--- a/geom/gdml/inc/TGDMLWrite.h
+++ b/geom/gdml/inc/TGDMLWrite.h
@@ -13,6 +13,7 @@
 #define ROOT_TGDMLWRITE
 
 #include "TGeoMatrix.h"
+#include "TGeoElement.h"
 #include "TXMLEngine.h"
 #include "TGeoVolume.h"
 #include "TGeoParaboloid.h"
diff --git a/geom/geom/inc/TGeoAtt.h b/geom/geom/inc/TGeoAtt.h
index bbcc6e723afb3..9d7029e98c6fb 100644
--- a/geom/geom/inc/TGeoAtt.h
+++ b/geom/geom/inc/TGeoAtt.h
@@ -12,7 +12,7 @@
 #ifndef ROOT_TGeoAtt
 #define ROOT_TGeoAtt
 
-#include "TObject.h"
+#include "Rtypes.h"
 
 class TGeoAtt
 {
diff --git a/geom/geom/inc/TGeoBoolNode.h b/geom/geom/inc/TGeoBoolNode.h
index 36d6c6159077b..72670a5d09b9b 100644
--- a/geom/geom/inc/TGeoBoolNode.h
+++ b/geom/geom/inc/TGeoBoolNode.h
@@ -12,10 +12,11 @@
 #ifndef ROOT_TGeoBoolNode
 #define ROOT_TGeoBoolNode
 
-#include <mutex>
-
 #include "TObject.h"
 
+#include <mutex>
+#include <vector>
+
 // forward declarations
 class TGeoShape;
 class TGeoMatrix;
diff --git a/geom/geom/inc/TGeoCache.h b/geom/geom/inc/TGeoCache.h
index 2b6bbb4214c6d..eb8242e960c49 100644
--- a/geom/geom/inc/TGeoCache.h
+++ b/geom/geom/inc/TGeoCache.h
@@ -15,7 +15,11 @@
 
 #include "TGeoNode.h"
 
+#ifdef R__LESS_INCLUDES
+struct TGeoStateInfo;
+#else
 #include "TGeoStateInfo.h"
+#endif
 
 // forward declarations
 class TGeoManager;
diff --git a/geom/geom/inc/TGeoManager.h b/geom/geom/inc/TGeoManager.h
index 9b1796c27d8ec..29f81c65dcc28 100644
--- a/geom/geom/inc/TGeoManager.h
+++ b/geom/geom/inc/TGeoManager.h
@@ -14,7 +14,9 @@
 
 #include <mutex>
 #include <thread>
+#include <map>
 
+#include "TNamed.h"
 #include "TObjArray.h"
 #include "TGeoNavigator.h"
 
diff --git a/geom/geom/inc/TGeoMaterial.h b/geom/geom/inc/TGeoMaterial.h
index c5cdb681c7794..641201adefd36 100644
--- a/geom/geom/inc/TGeoMaterial.h
+++ b/geom/geom/inc/TGeoMaterial.h
@@ -16,7 +16,12 @@
 #include <TAttFill.h>
 #include <TList.h>
 
+#ifdef R__LESS_INCLUDES
+class TGeoElement;
+class TGeoElementTable;
+#else
 #include "TGeoElement.h"
+#endif
 
 // forward declarations
 class TGeoExtension;
diff --git a/geom/geom/inc/TGeoParallelWorld.h b/geom/geom/inc/TGeoParallelWorld.h
index 2d8665884efc0..e68857280a7a3 100644
--- a/geom/geom/inc/TGeoParallelWorld.h
+++ b/geom/geom/inc/TGeoParallelWorld.h
@@ -11,8 +11,7 @@
 #ifndef ROOT_TGeoParallelWorld
 #define ROOT_TGeoParallelWorld
 
-
-#include "TGeoVolume.h"
+#include "TNamed.h"
 
 // forward declarations
 class TGeoManager;
diff --git a/geom/geom/inc/TGeoPatternFinder.h b/geom/geom/inc/TGeoPatternFinder.h
index 0e3c9f450e9fb..b8f4b509ddd6b 100644
--- a/geom/geom/inc/TGeoPatternFinder.h
+++ b/geom/geom/inc/TGeoPatternFinder.h
@@ -12,12 +12,12 @@
 #ifndef ROOT_TGeoPatternFinder
 #define ROOT_TGeoPatternFinder
 
-#include <mutex>
-
 #include "TObject.h"
 
-#include "TGeoVolume.h"
+#include <mutex>
+#include <vector>
 
+#include "TGeoVolume.h"
 
 class TGeoMatrix;
 
diff --git a/geom/geom/inc/TGeoPgon.h b/geom/geom/inc/TGeoPgon.h
index 14276672fb394..9846038fe1ff9 100644
--- a/geom/geom/inc/TGeoPgon.h
+++ b/geom/geom/inc/TGeoPgon.h
@@ -12,10 +12,11 @@
 #ifndef ROOT_TGeoPgon
 #define ROOT_TGeoPgon
 
-#include <mutex>
-
 #include "TGeoPcon.h"
 
+#include <mutex>
+#include <vector>
+
 class TGeoPgon : public TGeoPcon
 {
 public:
diff --git a/geom/geom/inc/TGeoPhysicalNode.h b/geom/geom/inc/TGeoPhysicalNode.h
index a00467740ebd8..3691f42733332 100644
--- a/geom/geom/inc/TGeoPhysicalNode.h
+++ b/geom/geom/inc/TGeoPhysicalNode.h
@@ -14,8 +14,6 @@
 
 #include "TNamed.h"
 
-#include "TObjArray.h"
-
 #include "TAttLine.h"
 
 // forward declarations
@@ -25,6 +23,7 @@ class TGeoVolume;
 class TGeoNode;
 class TGeoShape;
 class TGeoNavigator;
+class TObjArray;
 
 //////////////////////////////////////////////////////////////////////////////
 //                                                                          //
diff --git a/geom/geom/inc/TGeoRCPtr.h b/geom/geom/inc/TGeoRCPtr.h
index 7718a800a5e44..4313485877e93 100644
--- a/geom/geom/inc/TGeoRCPtr.h
+++ b/geom/geom/inc/TGeoRCPtr.h
@@ -9,6 +9,9 @@
  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
  *************************************************************************/
 
+#ifndef ROOT_TGeoRCPtr
+#define ROOT_TGeoRCPtr
+
 /** \class TGeoRCPtr
 \ingroup Geometry_classes
 
@@ -114,3 +117,5 @@ class TGeoRCPtr
 private:
    T *fPtr;   //Actual pointer
 };
+
+#endif
diff --git a/geom/geom/inc/TGeoTypedefs.h b/geom/geom/inc/TGeoTypedefs.h
index 8a77ec597f04b..4af53e6c1f872 100644
--- a/geom/geom/inc/TGeoTypedefs.h
+++ b/geom/geom/inc/TGeoTypedefs.h
@@ -9,6 +9,9 @@
  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
  *************************************************************************/
 
+#ifndef ROOT_TGeoTypedefs
+#define ROOT_TGeoTypedefs
+
 /// Typedefs used by the geometry group
 #include <vector>
 
@@ -18,3 +21,5 @@ namespace Tessellated {
   using VertexVec_t = std::vector<Vertex_t>;
 
 } // namespace Tessellated
+
+#endif
diff --git a/geom/geom/inc/TGeoVector3.h b/geom/geom/inc/TGeoVector3.h
index abd0fbc049bed..c89a1718ec4dc 100644
--- a/geom/geom/inc/TGeoVector3.h
+++ b/geom/geom/inc/TGeoVector3.h
@@ -9,8 +9,8 @@
  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
  *************************************************************************/
 
-#ifndef ROOT_Vertex_t
-#define ROOT_Vertex_t
+#ifndef ROOT_TGeoVector3
+#define ROOT_TGeoVector3
 
 #include <Riostream.h>
 #include <TMath.h>
diff --git a/geom/geom/inc/TGeoVolume.h b/geom/geom/inc/TGeoVolume.h
index e023c2dca9874..c336e61fa8e46 100644
--- a/geom/geom/inc/TGeoVolume.h
+++ b/geom/geom/inc/TGeoVolume.h
@@ -13,8 +13,8 @@
 #ifndef ROOT_TGeoVolume
 #define ROOT_TGeoVolume
 
-#include <mutex>
 
+#include "TNamed.h"
 #include "TGeoAtt.h"
 #include "TAttLine.h"
 #include "TAttFill.h"
@@ -22,6 +22,8 @@
 #include "TObjArray.h"
 #include "TGeoMedium.h"
 #include "TGeoShape.h"
+#include <mutex>
+#include <vector>
 
 // forward declarations
 class TH2F;
diff --git a/geom/geom/inc/TGeoXtru.h b/geom/geom/inc/TGeoXtru.h
index 3d019eec27cb1..62809e06741f8 100644
--- a/geom/geom/inc/TGeoXtru.h
+++ b/geom/geom/inc/TGeoXtru.h
@@ -12,10 +12,11 @@
 #ifndef ROOT_TGeoXtru
 #define ROOT_TGeoXtru
 
-#include <mutex>
-
 #include "TGeoBBox.h"
 
+#include <mutex>
+#include <vector>
+
 class TGeoPolygon;
 
 class TGeoXtru : public TGeoBBox
diff --git a/geom/geom/src/TGeoCache.cxx b/geom/geom/src/TGeoCache.cxx
index 0991efe245b53..b00781e4f0702 100644
--- a/geom/geom/src/TGeoCache.cxx
+++ b/geom/geom/src/TGeoCache.cxx
@@ -11,8 +11,8 @@
 
 #include "TGeoCache.h"
 
-#include "Rtypes.h"
 #include "TGeoManager.h"
+#include "TGeoStateInfo.h"
 #include "TGeoMatrix.h"
 #include "TGeoVolume.h"
 #include "TObject.h"
diff --git a/geom/geom/src/TGeoGlobalMagField.cxx b/geom/geom/src/TGeoGlobalMagField.cxx
index 1844d7aa03506..d75b616a52347 100644
--- a/geom/geom/src/TGeoGlobalMagField.cxx
+++ b/geom/geom/src/TGeoGlobalMagField.cxx
@@ -8,9 +8,11 @@
  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
  *************************************************************************/
 
-#include "TROOT.h"
 #include "TGeoGlobalMagField.h"
 
+#include "TROOT.h"
+#include "TList.h"
+
 /** \class TGeoGlobalMagField
 \ingroup Geometry_classes
 
diff --git a/geom/geom/src/TGeoMaterial.cxx b/geom/geom/src/TGeoMaterial.cxx
index 4ebfdf7eaf29b..e7d05aa04d437 100644
--- a/geom/geom/src/TGeoMaterial.cxx
+++ b/geom/geom/src/TGeoMaterial.cxx
@@ -20,8 +20,7 @@ Base class describing materials.
 #include "Riostream.h"
 #include "TMath.h"
 #include "TObjArray.h"
-#include "TStyle.h"
-#include "TList.h"
+#include "TGeoElement.h"
 #include "TGeoManager.h"
 #include "TGeoExtension.h"
 #include "TGeoMaterial.h"
diff --git a/geom/geombuilder/src/TGeoMaterialEditor.cxx b/geom/geombuilder/src/TGeoMaterialEditor.cxx
index 65119611afa69..aa0fb6c37e101 100644
--- a/geom/geombuilder/src/TGeoMaterialEditor.cxx
+++ b/geom/geombuilder/src/TGeoMaterialEditor.cxx
@@ -20,6 +20,7 @@ Editors for materials.
 #include "TGeoMaterialEditor.h"
 #include "TGeoTabManager.h"
 #include "TGeoMaterial.h"
+#include "TGeoElement.h"
 #include "TGeoManager.h"
 #include "TVirtualGeoPainter.h"
 #include "TView.h"
diff --git a/geom/geompainter/inc/TGeoTrack.h b/geom/geompainter/inc/TGeoTrack.h
index a141d150cc6eb..6bf154191ec18 100644
--- a/geom/geompainter/inc/TGeoTrack.h
+++ b/geom/geompainter/inc/TGeoTrack.h
@@ -14,10 +14,6 @@
 
 #include "TVirtualGeoTrack.h"
 
-#include "TPolyLine3D.h"
-
-class TPolyMarker3D;
-
 /////////////////////////////////////////////////////////////////////////////
 // TGeoTrack - Tracks attached to a geometry.                              //
 //             Tracks are 3D objects made of points and they store a       //
diff --git a/geom/geompainter/src/TGeoPainter.cxx b/geom/geompainter/src/TGeoPainter.cxx
index 7f471e0c702b9..da7ee92463b78 100644
--- a/geom/geompainter/src/TGeoPainter.cxx
+++ b/geom/geompainter/src/TGeoPainter.cxx
@@ -25,6 +25,7 @@ using TBuffer3D mechanism.
 #include "TAttFill.h"
 #include "TVirtualPad.h"
 #include "TCanvas.h"
+#include "TCanvasImp.h"
 #include "TH2F.h"
 #include "TF1.h"
 #include "TGraph.h"
@@ -37,6 +38,7 @@ using TBuffer3D mechanism.
 #include "TGeoAtt.h"
 #include "TGeoVolume.h"
 #include "TGeoNode.h"
+#include "TGeoElement.h"
 #include "TGeoManager.h"
 #include "TGeoTrack.h"
 #include "TGeoOverlap.h"
diff --git a/graf2d/gpad/inc/TCanvas.h b/graf2d/gpad/inc/TCanvas.h
index bf3d10d54302b..67b99ab8f53e8 100644
--- a/graf2d/gpad/inc/TCanvas.h
+++ b/graf2d/gpad/inc/TCanvas.h
@@ -16,13 +16,9 @@
 
 #include "TAttCanvas.h"
 
-#include "TString.h"
-
-#include "TCanvasImp.h"
-
+class TCanvasImp;
 class TContextMenu;
 class TControlBar;
-class TBrowser;
 
 class TCanvas : public TPad {
 
@@ -130,7 +126,7 @@ friend class TInterpreter;
    void              FeedbackMode(Bool_t set);
    void              Flush();
    void              UseCurrentStyle(); // *MENU*
-   void              ForceUpdate() { if (fCanvasImp) fCanvasImp->ForceUpdate(); }
+   void              ForceUpdate();
    const char       *GetDISPLAY() const {return fDISPLAY.Data();}
    TContextMenu     *GetContextMenu() const {return fContextMenu;};
    Int_t             GetDoubleBuffer() const {return fDoubleBuffer;}
@@ -169,13 +165,13 @@ friend class TInterpreter;
    virtual void      HandleInput(EEventType button, Int_t x, Int_t y);
    Bool_t            HasMenuBar() const { return TestBit(kMenuBar); }
    virtual void      HighlightConnect(const char *slot);
-   void              Iconify() { if (fCanvasImp) fCanvasImp->Iconify(); }
+   void              Iconify();
    Bool_t            IsBatch() const { return fBatch; }
    Bool_t            IsDrawn() { return fDrawn; }
    Bool_t            IsFolder() const;
    Bool_t            IsGrayscale();
    Bool_t            IsRetained() const { return fRetained; }
-   Bool_t            IsWeb() const { return fCanvasImp ? fCanvasImp->IsWeb() : kFALSE; }
+   Bool_t            IsWeb() const;
    virtual void      ls(Option_t *option="") const;
    void              MoveOpaque(Int_t set=1);
    Bool_t            OpaqueMoving() const { return TestBit(kMoveOpaque); }
@@ -189,7 +185,7 @@ friend class TInterpreter;
    virtual void      Selected(TVirtualPad *pad, TObject *obj, Int_t event);            // *SIGNAL*
    virtual void      Cleared(TVirtualPad *pad);                                        // *SIGNAL*
    virtual void      Closed();                                                         // *SIGNAL*
-   void              RaiseWindow() { if (fCanvasImp) fCanvasImp->RaiseWindow(); }
+   void              RaiseWindow();
    void              ResetDrawn() { fDrawn=kFALSE; }
    virtual void      Resize(Option_t *option="");
    void              ResizeOpaque(Int_t set=1);
@@ -200,14 +196,8 @@ friend class TInterpreter;
    virtual void      SetName(const char *name="");
    virtual void      SetFixedAspectRatio(Bool_t fixed = kTRUE);  // *TOGGLE*
    void              SetGrayscale(Bool_t set = kTRUE); // *TOGGLE* *GETTER=IsGrayscale
-   void              SetWindowPosition(Int_t x, Int_t y) { if (fCanvasImp) fCanvasImp->SetWindowPosition(x, y); }
-   void SetWindowSize(UInt_t ww, UInt_t wh)
-   {
-      if (fBatch)
-         SetCanvasSize((ww + fCw) / 2, (wh + fCh) / 2);
-      else if (fCanvasImp)
-         fCanvasImp->SetWindowSize(ww, wh);
-   }
+   void              SetWindowPosition(Int_t x, Int_t y);
+   void              SetWindowSize(UInt_t ww, UInt_t wh);
    void              SetCanvasImp(TCanvasImp *i) { fCanvasImp = i; }
    void              SetCanvasSize(UInt_t ww, UInt_t wh); // *MENU*
    void              SetHighLightColor(Color_t col) { fHighLightColor = col; }
@@ -215,7 +205,7 @@ friend class TInterpreter;
    void              SetClickSelected(TObject *obj) { fClickSelected = obj; }
    void              SetSelectedPad(TPad *pad) { fSelectedPad = pad; }
    void              SetClickSelectedPad(TPad *pad) { fClickSelectedPad = pad; }
-   void              Show() { if (fCanvasImp) fCanvasImp->Show(); }
+   void              Show();
    virtual void      Size(Float_t xsizeuser=0, Float_t ysizeuser=0);
    void              SetBatch(Bool_t batch=kTRUE);
    static  void      SetFolder(Bool_t isfolder=kTRUE);
diff --git a/graf2d/gpad/inc/TControlBar.h b/graf2d/gpad/inc/TControlBar.h
index ed6d7638b9a74..95b546335ffdb 100644
--- a/graf2d/gpad/inc/TControlBar.h
+++ b/graf2d/gpad/inc/TControlBar.h
@@ -12,10 +12,14 @@
 #ifndef ROOT_TControlBar
 #define ROOT_TControlBar
 
-
 #include "TControlBarButton.h"
 
+#ifdef R__LESS_INCLUDES
+class TObjArray;
+class TControlBarImp;
+#else
 #include "TControlBarImp.h"
+#endif
 
 class TList;
 
diff --git a/graf2d/gpad/inc/TControlBarButton.h b/graf2d/gpad/inc/TControlBarButton.h
index 6450b6503a11e..0da8518b4eab5 100644
--- a/graf2d/gpad/inc/TControlBarButton.h
+++ b/graf2d/gpad/inc/TControlBarButton.h
@@ -12,12 +12,8 @@
 #ifndef ROOT_TControlBarButton
 #define ROOT_TControlBarButton
 
-
-#include "Rtypes.h"
-
 #include "TNamed.h"
 
-
 class TControlBarButton : public TNamed {
 
 protected:
diff --git a/graf2d/gpad/inc/TCreatePrimitives.h b/graf2d/gpad/inc/TCreatePrimitives.h
index 688bdce9580d3..9183c26026ca8 100644
--- a/graf2d/gpad/inc/TCreatePrimitives.h
+++ b/graf2d/gpad/inc/TCreatePrimitives.h
@@ -12,8 +12,6 @@
 #define ROOT_TCreatePrimitives
 
 
-#include "Rtypes.h"
-
 #include "TLatex.h"
 #include "TCurlyArc.h"
 #include "TArrow.h"
diff --git a/graf2d/gpad/inc/TPad.h b/graf2d/gpad/inc/TPad.h
index 4876a47e2ead4..99beae713c26f 100644
--- a/graf2d/gpad/inc/TPad.h
+++ b/graf2d/gpad/inc/TPad.h
@@ -12,11 +12,8 @@
 #ifndef ROOT_TPad
 #define ROOT_TPad
 
-
 #include "TVirtualPad.h"
 #include "TAttBBox2D.h"
-#include "TPoint.h"
-#include "GuiTypes.h"
 
 class TVirtualViewer3D;
 class TVirtualPadPainter;
@@ -24,7 +21,7 @@ class TBrowser;
 class TBox;
 class TLegend;
 class TArrow;
-
+class TPoint;
 
 class TPad : public TVirtualPad, public TAttBBox2D {
 
diff --git a/graf2d/gpad/inc/TPaveClass.h b/graf2d/gpad/inc/TPaveClass.h
index 6686340817af8..0d70001c6f660 100644
--- a/graf2d/gpad/inc/TPaveClass.h
+++ b/graf2d/gpad/inc/TPaveClass.h
@@ -13,8 +13,12 @@
 
 
 #include "TPaveLabel.h"
-#include "TClassTree.h"
 
+#ifdef R__LESS_INCLUDES
+class TClassTree;
+#else
+#include "TClassTree.h"
+#endif
 
 class TPaveClass : public TPaveLabel{
 
diff --git a/graf2d/gpad/src/TCanvas.cxx b/graf2d/gpad/src/TCanvas.cxx
index 1c86d84d3fa44..098f61120c0df 100644
--- a/graf2d/gpad/src/TCanvas.cxx
+++ b/graf2d/gpad/src/TCanvas.cxx
@@ -16,6 +16,7 @@
 #include "TROOT.h"
 #include "TBuffer.h"
 #include "TCanvas.h"
+#include "TCanvasImp.h"
 #include "TDatime.h"
 #include "TClass.h"
 #include "TStyle.h"
@@ -1155,6 +1156,14 @@ void TCanvas::Flush()
    if (padsav) padsav->cd();
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Force canvas update
+
+void TCanvas::ForceUpdate()
+{
+   if (fCanvasImp) fCanvasImp->ForceUpdate();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Force a copy of current style for all objects in canvas.
 
@@ -1448,6 +1457,15 @@ void TCanvas::HandleInput(EEventType event, Int_t px, Int_t py)
    }
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Iconify canvas
+
+void TCanvas::Iconify()
+{
+   if (fCanvasImp)
+      fCanvasImp->Iconify();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Is folder ?
 
@@ -1456,6 +1474,14 @@ Bool_t TCanvas::IsFolder() const
    return fgIsFolder;
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Is web canvas
+
+Bool_t TCanvas::IsWeb() const
+{
+   return fCanvasImp ? fCanvasImp->IsWeb() : kFALSE;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// List all pads.
 
@@ -1710,6 +1736,16 @@ void TCanvas::Resize(Option_t *)
    if (padsav) padsav->cd();
 }
 
+
+////////////////////////////////////////////////////////////////////////////////
+/// Raise canvas window
+
+void TCanvas::RaiseWindow()
+{
+   if (fCanvasImp)
+      fCanvasImp->RaiseWindow();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Set option to resize objects/pads in a canvas.
 ///
@@ -2144,6 +2180,26 @@ void TCanvas::SetTitle(const char *title)
    if (fCanvasImp) fCanvasImp->SetWindowTitle(title);
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Set canvas window position
+
+void TCanvas::SetWindowPosition(Int_t x, Int_t y)
+{
+   if (fCanvasImp)
+      fCanvasImp->SetWindowPosition(x, y);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+/// Set canvas window size
+
+void TCanvas::SetWindowSize(UInt_t ww, UInt_t wh)
+{
+   if (fBatch)
+      SetCanvasSize((ww + fCw) / 2, (wh + fCh) / 2);
+   else if (fCanvasImp)
+      fCanvasImp->SetWindowSize(ww, wh);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Set the canvas scale in centimeters.
 ///
@@ -2172,6 +2228,15 @@ void TCanvas::Size(Float_t xsize, Float_t ysize)
    Resize();
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Show canvas
+
+void TCanvas::Show()
+{
+   if (fCanvasImp)
+      fCanvasImp->Show();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Stream a class object.
 
diff --git a/graf2d/gpad/src/TControlBar.cxx b/graf2d/gpad/src/TControlBar.cxx
index f9dd3225a905f..723c0121df81f 100644
--- a/graf2d/gpad/src/TControlBar.cxx
+++ b/graf2d/gpad/src/TControlBar.cxx
@@ -78,6 +78,7 @@ will return the name of the last clicked button.
 
 #include "TApplication.h"
 #include "TControlBar.h"
+#include "TControlBarImp.h"
 #include "TGuiFactory.h"
 #include "TList.h"
 #include "TStyle.h"
diff --git a/graf2d/gpad/src/TPaveClass.cxx b/graf2d/gpad/src/TPaveClass.cxx
index 5ca4838d11c6b..a58549a71b414 100644
--- a/graf2d/gpad/src/TPaveClass.cxx
+++ b/graf2d/gpad/src/TPaveClass.cxx
@@ -12,6 +12,7 @@
 #include "TROOT.h"
 #include "Buttons.h"
 #include "TPaveClass.h"
+#include "TClassTree.h"
 
 ClassImp(TPaveClass);
 
diff --git a/graf2d/graf/inc/TArc.h b/graf2d/graf/inc/TArc.h
index d699439bf0404..dc09c570c3f9b 100644
--- a/graf2d/graf/inc/TArc.h
+++ b/graf2d/graf/inc/TArc.h
@@ -21,10 +21,8 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "Rtypes.h"
 #include "TEllipse.h"
 
-
 class TArc : public TEllipse {
 
 public:
diff --git a/graf2d/graf/inc/TBox.h b/graf2d/graf/inc/TBox.h
index 8fa3206a61b34..e62045bb71e37 100644
--- a/graf2d/graf/inc/TBox.h
+++ b/graf2d/graf/inc/TBox.h
@@ -12,14 +12,12 @@
 #ifndef ROOT_TBox
 #define ROOT_TBox
 
-
 #include "TObject.h"
 #include "TAttLine.h"
 #include "TAttFill.h"
 #include "TAttBBox2D.h"
-#include "TPoint.h"
-#include "GuiTypes.h"
 
+class TPoint;
 
 class TBox : public TObject, public TAttLine, public TAttFill, public TAttBBox2D {
 
diff --git a/graf2d/graf/inc/TCurlyArc.h b/graf2d/graf/inc/TCurlyArc.h
index 3341c72c2536e..0107c845ec91d 100644
--- a/graf2d/graf/inc/TCurlyArc.h
+++ b/graf2d/graf/inc/TCurlyArc.h
@@ -11,12 +11,10 @@
 #ifndef ROOT_TCurlyArc
 #define ROOT_TCurlyArc
 
-#include "GuiTypes.h"
+#include "TCurlyLine.h"
 
 class TPoint;
 
-#include "TCurlyLine.h"
-
 class TCurlyArc : public TCurlyLine {
 
 private:
diff --git a/graf2d/graf/inc/TCurlyLine.h b/graf2d/graf/inc/TCurlyLine.h
index 76500e20b5ebe..c23e29d2526b0 100644
--- a/graf2d/graf/inc/TCurlyLine.h
+++ b/graf2d/graf/inc/TCurlyLine.h
@@ -11,14 +11,12 @@
 #ifndef ROOT_TCurlyLine
 #define ROOT_TCurlyLine
 
-
 #include "TPolyLine.h"
 #include "TAttBBox2D.h"
-#include "GuiTypes.h"
 
 class TPoint;
 
-class TCurlyLine : public TPolyLine , public TAttBBox2D {
+class TCurlyLine : public TPolyLine, public TAttBBox2D {
 
 protected:
    Double_t fX1;             ///< start x, center for arc
diff --git a/graf2d/graf/inc/TEllipse.h b/graf2d/graf/inc/TEllipse.h
index 6338b194e56fd..c55b80c0e2597 100644
--- a/graf2d/graf/inc/TEllipse.h
+++ b/graf2d/graf/inc/TEllipse.h
@@ -17,9 +17,8 @@
 #include "TAttLine.h"
 #include "TAttFill.h"
 #include "TAttBBox2D.h"
-#include "TPoint.h"
-#include "GuiTypes.h"
 
+class TPoint;
 
 class TEllipse : public TObject, public TAttLine, public TAttFill, public TAttBBox2D {
 
diff --git a/graf2d/graf/inc/TGaxis.h b/graf2d/graf/inc/TGaxis.h
index e84134c605907..bb8b069b781e5 100644
--- a/graf2d/graf/inc/TGaxis.h
+++ b/graf2d/graf/inc/TGaxis.h
@@ -12,10 +12,9 @@
 #ifndef ROOT_TGaxis
 #define ROOT_TGaxis
 
-
-#include "TNamed.h"
 #include "TLine.h"
 #include "TAttText.h"
+#include "TString.h"
 
 class TF1;
 class TAxis;
diff --git a/graf2d/graf/inc/TGraphPolar.h b/graf2d/graf/inc/TGraphPolar.h
index 4ffe73d3045ba..b83e785dda396 100644
--- a/graf2d/graf/inc/TGraphPolar.h
+++ b/graf2d/graf/inc/TGraphPolar.h
@@ -13,11 +13,12 @@
 #define ROOT_TGraphPolar
 
 #include "TGraphErrors.h"
-#include "TAttText.h"
-#include "TAttLine.h"
 
+#ifdef R__LESS_INCLUDES
+class TGraphPolargram;
+#else
 #include "TGraphPolargram.h"
-
+#endif
 
 class TGraphPolar: public TGraphErrors {
 
diff --git a/graf2d/graf/inc/TLine.h b/graf2d/graf/inc/TLine.h
index d6bbe9945baf6..d4baac5198db5 100644
--- a/graf2d/graf/inc/TLine.h
+++ b/graf2d/graf/inc/TLine.h
@@ -16,9 +16,8 @@
 #include "TObject.h"
 #include "TAttLine.h"
 #include "TAttBBox2D.h"
-#include "TPoint.h"
-#include "GuiTypes.h"
 
+class TPoint;
 
 class TLine : public TObject, public TAttLine, public TAttBBox2D {
 
diff --git a/graf2d/graf/inc/TMarker.h b/graf2d/graf/inc/TMarker.h
index 4764ff1688e36..8591eb5457fcc 100644
--- a/graf2d/graf/inc/TMarker.h
+++ b/graf2d/graf/inc/TMarker.h
@@ -13,10 +13,9 @@
 #define ROOT_TMarker
 
 
+#include "TObject.h"
 #include "TAttMarker.h"
-#include "TNamed.h"
 #include "TAttBBox2D.h"
-#include "GuiTypes.h"
 
 class TPoint;
 
diff --git a/graf2d/graf/inc/TPaveText.h b/graf2d/graf/inc/TPaveText.h
index 6b1bf1efb18eb..81807c24e6ec8 100644
--- a/graf2d/graf/inc/TPaveText.h
+++ b/graf2d/graf/inc/TPaveText.h
@@ -15,8 +15,8 @@
 
 #include "TPave.h"
 #include "TText.h"
-#include "TLine.h"
 
+class TLine;
 
 class TPaveText : public TPave, public TAttText {
 
diff --git a/graf2d/graf/inc/TPieSlice.h b/graf2d/graf/inc/TPieSlice.h
index d86b209106f1a..561a6f15937f3 100644
--- a/graf2d/graf/inc/TPieSlice.h
+++ b/graf2d/graf/inc/TPieSlice.h
@@ -8,12 +8,12 @@
 
 #ifndef ROOT_TPieSlice
 #define ROOT_TPieSlice
-#include "TObject.h"
-#include <TString.h>
-#include <TAttText.h>
+
+#include <TNamed.h>
 #include <TAttFill.h>
 #include <TAttLine.h>
-#include <TPie.h>
+
+class TPie;
 
 class TPieSlice : public TNamed, public TAttFill, public TAttLine {
 
diff --git a/graf2d/graf/inc/TText.h b/graf2d/graf/inc/TText.h
index 74e0023caf91d..a4fde5e38d780 100644
--- a/graf2d/graf/inc/TText.h
+++ b/graf2d/graf/inc/TText.h
@@ -16,9 +16,8 @@
 #include "TAttText.h"
 #include "TNamed.h"
 #include "TAttBBox2D.h"
-#include "TPoint.h"
-#include "GuiTypes.h"
 
+class TPoint;
 
 class TText : public TNamed, public TAttText, public TAttBBox2D {
 
diff --git a/graf2d/graf/src/TLegend.cxx b/graf2d/graf/src/TLegend.cxx
index 92722e1c9efde..7a08f6d563ecc 100644
--- a/graf2d/graf/src/TLegend.cxx
+++ b/graf2d/graf/src/TLegend.cxx
@@ -26,6 +26,7 @@
 #include "Riostream.h"
 #include "TMultiGraph.h"
 #include "TGraph.h"
+#include "TH1.h"
 #include "THStack.h"
 
 ClassImp(TLegend);
diff --git a/graf2d/graf/src/TPaveText.cxx b/graf2d/graf/src/TPaveText.cxx
index e49b5c10580f2..c7cc620bc9734 100644
--- a/graf2d/graf/src/TPaveText.cxx
+++ b/graf2d/graf/src/TPaveText.cxx
@@ -25,6 +25,7 @@
 #include "TError.h"
 #include "TColor.h"
 #include "TClass.h"
+#include "TLine.h"
 
 ClassImp(TPaveText);
 
diff --git a/graf2d/graf/src/TPie.cxx b/graf2d/graf/src/TPie.cxx
index 1bf03cbc5ec62..a7927d9b15d7d 100644
--- a/graf2d/graf/src/TPie.cxx
+++ b/graf2d/graf/src/TPie.cxx
@@ -24,6 +24,7 @@
 #include <TPaveText.h>
 #include <TH1.h>
 #include <TColor.h>
+#include <TLine.h>
 
 ClassImp(TPie);
 
diff --git a/graf2d/graf/src/TPieSlice.cxx b/graf2d/graf/src/TPieSlice.cxx
index def68ebf32b02..08925fbacf91d 100644
--- a/graf2d/graf/src/TPieSlice.cxx
+++ b/graf2d/graf/src/TPieSlice.cxx
@@ -18,6 +18,7 @@
 #include <TLatex.h>
 #include <TPaveText.h>
 #include <TH1.h>
+#include <TPie.h>
 
 ClassImp(TPieSlice);
 
diff --git a/graf2d/primitivesv7/inc/ROOT/RBox.hxx b/graf2d/primitivesv7/inc/ROOT/RBox.hxx
index 44aeaef92a4bb..7050cde00863f 100644
--- a/graf2d/primitivesv7/inc/ROOT/RBox.hxx
+++ b/graf2d/primitivesv7/inc/ROOT/RBox.hxx
@@ -14,7 +14,7 @@
 #include <ROOT/RPadPos.hxx>
 
 #include <initializer_list>
-#include <memory>
+
 
 namespace ROOT {
 namespace Experimental {
diff --git a/graf2d/primitivesv7/inc/ROOT/RFrameTitle.hxx b/graf2d/primitivesv7/inc/ROOT/RFrameTitle.hxx
index ef85964a38d49..cbf624cf9112e 100644
--- a/graf2d/primitivesv7/inc/ROOT/RFrameTitle.hxx
+++ b/graf2d/primitivesv7/inc/ROOT/RFrameTitle.hxx
@@ -13,7 +13,6 @@
 #include <ROOT/RAttrText.hxx>
 #include <ROOT/RPadPos.hxx>
 
-#include <memory>
 #include <string>
 
 namespace ROOT {
diff --git a/graf2d/primitivesv7/inc/ROOT/RLine.hxx b/graf2d/primitivesv7/inc/ROOT/RLine.hxx
index 79c51acc006e0..b2098f2312c23 100644
--- a/graf2d/primitivesv7/inc/ROOT/RLine.hxx
+++ b/graf2d/primitivesv7/inc/ROOT/RLine.hxx
@@ -13,8 +13,6 @@
 #include <ROOT/RAttrLine.hxx>
 #include <ROOT/RPadPos.hxx>
 
-#include <memory>
-
 namespace ROOT {
 namespace Experimental {
 
diff --git a/graf2d/primitivesv7/inc/ROOT/RMarker.hxx b/graf2d/primitivesv7/inc/ROOT/RMarker.hxx
index 14b2522b6bfbb..8ef09946edf12 100644
--- a/graf2d/primitivesv7/inc/ROOT/RMarker.hxx
+++ b/graf2d/primitivesv7/inc/ROOT/RMarker.hxx
@@ -14,7 +14,6 @@
 #include <ROOT/RPadPos.hxx>
 
 #include <initializer_list>
-#include <memory>
 
 namespace ROOT {
 namespace Experimental {
diff --git a/graf2d/primitivesv7/inc/ROOT/RText.hxx b/graf2d/primitivesv7/inc/ROOT/RText.hxx
index 6e476ba36682a..aaa083d15a8a1 100644
--- a/graf2d/primitivesv7/inc/ROOT/RText.hxx
+++ b/graf2d/primitivesv7/inc/ROOT/RText.hxx
@@ -13,7 +13,6 @@
 #include <ROOT/RAttrText.hxx>
 #include <ROOT/RPadPos.hxx>
 
-#include <memory>
 #include <string>
 
 namespace ROOT {
diff --git a/graf2d/win32gdk/src/TGWin32GL.cxx b/graf2d/win32gdk/src/TGWin32GL.cxx
index fda6648361d84..a01f379da30ea 100644
--- a/graf2d/win32gdk/src/TGWin32GL.cxx
+++ b/graf2d/win32gdk/src/TGWin32GL.cxx
@@ -23,6 +23,7 @@ The TGWin32GL is win32gdk implementation of TVirtualGLImp class.
 #include "TVirtualX.h"
 #include "TError.h"
 #include "TROOT.h"
+#include "TList.h"
 
 #include "Windows4Root.h"
 #include "gdk/gdk.h"
diff --git a/graf2d/win32gdk/src/TGWin32VirtualGLProxy.cxx b/graf2d/win32gdk/src/TGWin32VirtualGLProxy.cxx
index 85242fd312a9e..0f84f6a76c25c 100644
--- a/graf2d/win32gdk/src/TGWin32VirtualGLProxy.cxx
+++ b/graf2d/win32gdk/src/TGWin32VirtualGLProxy.cxx
@@ -13,6 +13,7 @@
 #include "TGWin32VirtualGLProxy.h"
 #include "TGWin32.h"
 #include "TROOT.h"
+#include "TList.h"
 
 static TGLManager *gManager = 0;
 
diff --git a/graf3d/eve/inc/TEveGeoPolyShape.h b/graf3d/eve/inc/TEveGeoPolyShape.h
index 7f25eefef3d8d..a89f4ae80b450 100644
--- a/graf3d/eve/inc/TEveGeoPolyShape.h
+++ b/graf3d/eve/inc/TEveGeoPolyShape.h
@@ -12,7 +12,6 @@
 #ifndef ROOT_TEveGeoPolyShape
 #define ROOT_TEveGeoPolyShape
 
-#include "Rtypes.h"
 #include "TGeoBBox.h"
 
 #include <vector>
diff --git a/graf3d/eve7/src/REveDataClasses.cxx b/graf3d/eve7/src/REveDataClasses.cxx
index 629addc9b7b93..cff869725b75f 100644
--- a/graf3d/eve7/src/REveDataClasses.cxx
+++ b/graf3d/eve7/src/REveDataClasses.cxx
@@ -17,6 +17,7 @@
 #include "TMethodArg.h"
 #include "TColor.h"
 #include "TClass.h"
+#include "TList.h"
 #include "TBaseClass.h"
 
 #include "json.hpp"
diff --git a/graf3d/eve7/src/REveManager.cxx b/graf3d/eve7/src/REveManager.cxx
index 53c41bf8dae0b..9508c3ab6cd3b 100644
--- a/graf3d/eve7/src/REveManager.cxx
+++ b/graf3d/eve7/src/REveManager.cxx
@@ -21,6 +21,7 @@
 #include <ROOT/RLogger.hxx>
 
 #include "TGeoManager.h"
+#include "TGeoMatrix.h"
 #include "TObjString.h"
 #include "TROOT.h"
 #include "TFile.h"
diff --git a/graf3d/g3d/inc/TPolyLine3D.h b/graf3d/g3d/inc/TPolyLine3D.h
index 8f165630d8e4b..8826a086056f7 100644
--- a/graf3d/g3d/inc/TPolyLine3D.h
+++ b/graf3d/g3d/inc/TPolyLine3D.h
@@ -22,11 +22,12 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TObject.h"
-#include "TList.h"
 #include "TString.h"
 #include "TAttLine.h"
 #include "TAtt3D.h"
 
+class TList;
+
 
 class TPolyLine3D : public TObject, public TAttLine, public TAtt3D
 {
diff --git a/graf3d/gl/src/TGLVoxelPainter.cxx b/graf3d/gl/src/TGLVoxelPainter.cxx
index 9f24c4f7d5d20..c3046e10832f9 100644
--- a/graf3d/gl/src/TGLVoxelPainter.cxx
+++ b/graf3d/gl/src/TGLVoxelPainter.cxx
@@ -5,6 +5,7 @@
 #include "Buttons.h"
 #include "TString.h"
 #include "TROOT.h"
+#include "TList.h"
 #include "TClass.h"
 #include "TColor.h"
 #include "TStyle.h"
diff --git a/gui/gui/inc/TGFrame.h b/gui/gui/inc/TGFrame.h
index 6d5640ecc966b..55d54afb50853 100644
--- a/gui/gui/inc/TGFrame.h
+++ b/gui/gui/inc/TGFrame.h
@@ -29,12 +29,12 @@
 #include "TGFont.h"
 #include "TGLayout.h"
 #include "TGString.h"
-#include "TList.h"
 
 class TGResourcePool;
 class TGTextButton;
 class TGVFileSplitter;
 class TDNDData;
+class TList;
 
 //---- frame states
 
diff --git a/gui/gui/inc/TGListBox.h b/gui/gui/inc/TGListBox.h
index 6684d4f21a9e5..93ba4344743ff 100644
--- a/gui/gui/inc/TGListBox.h
+++ b/gui/gui/inc/TGListBox.h
@@ -35,10 +35,9 @@
 #include "TGFrame.h"
 #include "TGCanvas.h"
 #include "TGScrollBar.h"
-#include "TList.h"
 
 class TGListBox;
-
+class TList;
 
 //////////////////////////////////////////////////////////////////////////
 //                                                                      //
diff --git a/gui/gui/inc/TGPasswdDialog.h b/gui/gui/inc/TGPasswdDialog.h
index 560052adcce2e..6ccc34392f91b 100644
--- a/gui/gui/inc/TGPasswdDialog.h
+++ b/gui/gui/inc/TGPasswdDialog.h
@@ -40,8 +40,7 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TTime.h"
-#include "TString.h"
+#include "Rtypes.h"
 
 class TGTransientFrame;
 class TGTextButton;
diff --git a/gui/gui/src/TRootContextMenu.cxx b/gui/gui/src/TRootContextMenu.cxx
index 012f3cb1e0ece..050e6b8d06e17 100644
--- a/gui/gui/src/TRootContextMenu.cxx
+++ b/gui/gui/src/TRootContextMenu.cxx
@@ -35,6 +35,7 @@
 #include "TContextMenu.h"
 #include "TMethod.h"
 #include "TMethodArg.h"
+#include "TMethodCall.h"
 #include "TClass.h"
 #include "TVirtualX.h"
 #include "TCanvas.h"
diff --git a/gui/guibuilder/src/TGuiBldDragManager.cxx b/gui/guibuilder/src/TGuiBldDragManager.cxx
index daef031754366..7f80fadf66aea 100644
--- a/gui/guibuilder/src/TGuiBldDragManager.cxx
+++ b/gui/guibuilder/src/TGuiBldDragManager.cxx
@@ -25,7 +25,9 @@
 #include "TError.h"
 #include "TClassMenuItem.h"
 #include "TMethod.h"
+#include "TMethodCall.h"
 #include "TBaseClass.h"
+#include "TDataMember.h"
 #include "TMethodArg.h"
 #include "TToggle.h"
 #include "TDataType.h"
diff --git a/hist/hist/inc/TF1AbsComposition.h b/hist/hist/inc/TF1AbsComposition.h
index dacc545f59c84..e7c54260d492c 100644
--- a/hist/hist/inc/TF1AbsComposition.h
+++ b/hist/hist/inc/TF1AbsComposition.h
@@ -13,9 +13,6 @@
 
 #include "TObject.h"
 
-#include <iostream>
-#include <memory>
-
 class TF1AbsComposition : public TObject {
 
 public:
diff --git a/hist/hist/inc/TF1Convolution.h b/hist/hist/inc/TF1Convolution.h
index 7e0132295b73a..f550f2c938cac 100644
--- a/hist/hist/inc/TF1Convolution.h
+++ b/hist/hist/inc/TF1Convolution.h
@@ -11,11 +11,11 @@
 #ifndef ROOT_TF1Convolution__
 #define ROOT_TF1Convolution__
 
-#include <iostream>
+#include "TF1AbsComposition.h"
+#include <memory>
+#include <vector>
 #include "TF1.h"
 #include "TGraph.h"
-#include <memory>
-#include "TF1AbsComposition.h"
 
 class TF1Convolution : public TF1AbsComposition {
    std::unique_ptr<TF1> fFunction1;    ///< First function to be convolved
diff --git a/hist/hist/inc/TF1NormSum.h b/hist/hist/inc/TF1NormSum.h
index 56271099e87a9..e5081df39aafa 100644
--- a/hist/hist/inc/TF1NormSum.h
+++ b/hist/hist/inc/TF1NormSum.h
@@ -11,10 +11,10 @@
 #ifndef ROOT_TF1NormSum__
 #define ROOT_TF1NormSum__
 
-#include <iostream>
-#include "TF1.h"
-#include <memory>
 #include "TF1AbsComposition.h"
+#include <vector>
+#include <memory>
+#include "TF1.h"
 
 class TF1NormSum : public TF1AbsComposition {
 
diff --git a/hist/hist/inc/TFitResultPtr.h b/hist/hist/inc/TFitResultPtr.h
index aea45caeda1c9..510e271cd6b13 100644
--- a/hist/hist/inc/TFitResultPtr.h
+++ b/hist/hist/inc/TFitResultPtr.h
@@ -24,9 +24,10 @@
 
 #include "Rtypes.h"
 
-class TFitResult;
-
 #include <memory>
+#include <string>
+
+class TFitResult;
 
 class TFitResultPtr {
 public:
@@ -45,7 +46,7 @@ class TFitResultPtr {
 
    TFitResult* operator->() const;
 
-   TFitResult* Get() const; 
+   TFitResult* Get() const;
 
    TFitResultPtr& operator= (const TFitResultPtr& rhs);
 
diff --git a/hist/hist/inc/TFormula.h b/hist/hist/inc/TFormula.h
index 54722739ce5ea..6f10b6c5cf558 100644
--- a/hist/hist/inc/TFormula.h
+++ b/hist/hist/inc/TFormula.h
@@ -15,7 +15,6 @@
 
 #include "TNamed.h"
 #include "TBits.h"
-#include "TMethodCall.h"
 #include "TInterpreter.h"
 #include <cassert>
 #include <vector>
@@ -23,6 +22,9 @@
 #include <map>
 #include <Math/Types.h>
 
+class TMethodCall;
+
+
 class TFormulaFunction
 {
 public:
diff --git a/hist/hist/inc/THStack.h b/hist/hist/inc/THStack.h
index 3d2c96b9e3e66..f0fc746b723b7 100644
--- a/hist/hist/inc/THStack.h
+++ b/hist/hist/inc/THStack.h
@@ -21,9 +21,16 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TH1.h"
+#include "TNamed.h"
 #include "TObjArray.h"
 
+#ifdef R__LESS_INCLUDES
+class TH1;
+class TList;
+class TAxis;
+#else
+#include "TH1.h"
+#endif
 
 class TBrowser;
 class TFileMergeInfo;
diff --git a/hist/hist/inc/TMultiDimFit.h b/hist/hist/inc/TMultiDimFit.h
index 465ed89d0ca3c..18a671fb6334b 100644
--- a/hist/hist/inc/TMultiDimFit.h
+++ b/hist/hist/inc/TMultiDimFit.h
@@ -7,10 +7,10 @@
 #include "TNamed.h"
 #include "TVectorD.h"
 #include "TMatrixD.h"
-#include "TList.h"
 #include "TVirtualFitter.h"
 
 class TBrowser;
+class TList;
 
 class TMultiDimFit : public TNamed {
 
diff --git a/hist/hist/inc/TPrincipal.h b/hist/hist/inc/TPrincipal.h
index 7bf18beabd53e..85a585b646251 100644
--- a/hist/hist/inc/TPrincipal.h
+++ b/hist/hist/inc/TPrincipal.h
@@ -15,7 +15,8 @@
 #include "TNamed.h"
 #include "TVectorD.h"
 #include "TMatrixD.h"
-#include "TList.h"
+
+class TList;
 
 class TPrincipal : public TNamed {
 
diff --git a/hist/hist/inc/TSpline.h b/hist/hist/inc/TSpline.h
index e767545b07df6..6efb13f30e553 100644
--- a/hist/hist/inc/TSpline.h
+++ b/hist/hist/inc/TSpline.h
@@ -12,10 +12,19 @@
 #ifndef ROOT_TSpline
 #define ROOT_TSpline
 
+#ifdef R__LESS_INCLUDES
+#include "TNamed.h"
+#include "TAttLine.h"
+#include "TAttFill.h"
+#include "TAttMarker.h"
+#else
 #include "TGraph.h"
+#endif
 
 class TH1;
+class TH1F;
 class TF1;
+class TGraph;
 
 class TSpline : public TNamed, public TAttLine,
                 public TAttFill, public TAttMarker
@@ -124,7 +133,7 @@ class TSplinePoly3 : public TSplinePoly
    }
    Double_t Derivative(Double_t x) const {
       Double_t dx=x-fX;
-      return (fB+dx*(2*fC+3*fD*dx));      
+      return (fB+dx*(2*fC+3*fD*dx));
    }
 
 private:
diff --git a/hist/hist/inc/v5/TFormulaPrimitive.h b/hist/hist/inc/v5/TFormulaPrimitive.h
index 4156bff34cf95..a79c376bde214 100644
--- a/hist/hist/inc/v5/TFormulaPrimitive.h
+++ b/hist/hist/inc/v5/TFormulaPrimitive.h
@@ -25,12 +25,13 @@
 
 #include "TNamed.h"
 #include "TBits.h"
-#include "TObjArray.h"
+
+class TObjArray;
 
 namespace ROOT {
 
    namespace v5 {
-      
+
 class TFormula;
 
 class TFormulaPrimitive : public TNamed
@@ -96,5 +97,5 @@ class TFormulaPrimitive : public TNamed
 
 } // end namespace ROOT
 
-      
+
 #endif
diff --git a/hist/hist/src/TMultiDimFit.cxx b/hist/hist/src/TMultiDimFit.cxx
index 9f1c458f1ecd6..9eb2adf87a988 100644
--- a/hist/hist/src/TMultiDimFit.cxx
+++ b/hist/hist/src/TMultiDimFit.cxx
@@ -392,6 +392,7 @@
 #include "TH1.h"
 #include "TH2.h"
 #include "TROOT.h"
+#include "TList.h"
 #include "TBrowser.h"
 #include "TDecompChol.h"
 #include "TDatime.h"
diff --git a/hist/hist/src/TProfileHelper.h b/hist/hist/src/TProfileHelper.h
index 3e74837a1bc71..d5510b655effd 100644
--- a/hist/hist/src/TProfileHelper.h
+++ b/hist/hist/src/TProfileHelper.h
@@ -23,7 +23,6 @@
 
 #include "TH1.h"
 #include "TError.h"
-#include "TCollection.h"
 #include "THashList.h"
 #include "TMath.h"
 
diff --git a/hist/hist/src/TSpline.cxx b/hist/hist/src/TSpline.cxx
index b8674e7d62fcb..36a2c43826d41 100644
--- a/hist/hist/src/TSpline.cxx
+++ b/hist/hist/src/TSpline.cxx
@@ -15,6 +15,7 @@
 */
 
 #include "TROOT.h"
+#include "TGraph.h"
 #include "TBuffer.h"
 #include "TSpline.h"
 #include "TVirtualPad.h"
diff --git a/hist/unfold/src/TUnfold.cxx b/hist/unfold/src/TUnfold.cxx
index 37862937c1020..0f38e991e5284 100644
--- a/hist/unfold/src/TUnfold.cxx
+++ b/hist/unfold/src/TUnfold.cxx
@@ -119,6 +119,7 @@ along with TUnfold.  If not, see <http://www.gnu.org/licenses/>.
 #include <TMatrixDSymEigen.h>
 #include <TMath.h>
 #include "TUnfold.h"
+#include "TGraph.h"
 
 #include <map>
 #include <vector>
diff --git a/hist/unfold/src/TUnfoldDensity.cxx b/hist/unfold/src/TUnfoldDensity.cxx
index 8e2827247cf02..9b32da09613a4 100644
--- a/hist/unfold/src/TUnfoldDensity.cxx
+++ b/hist/unfold/src/TUnfoldDensity.cxx
@@ -151,6 +151,7 @@ whichever algorithm is used, the output has to be checked:
 #include "TUnfoldDensity.h"
 #include <TMath.h>
 #include <TVectorD.h>
+#include "TGraph.h"
 #include <iostream>
 #include <map>
 
diff --git a/html/inc/TClassDocOutput.h b/html/inc/TClassDocOutput.h
index a9752ae4e10ff..44c7aaee817a8 100644
--- a/html/inc/TClassDocOutput.h
+++ b/html/inc/TClassDocOutput.h
@@ -12,7 +12,6 @@
 #ifndef ROOT_TClassDocOutput
 #define ROOT_TClassDocOutput
 
-#include "Rtypes.h"
 #include "TDocOutput.h"
 
 class TDocParser;
diff --git a/io/io/inc/TDirectoryFile.h b/io/io/inc/TDirectoryFile.h
index de204fdb79aae..544ebc76431c6 100644
--- a/io/io/inc/TDirectoryFile.h
+++ b/io/io/inc/TDirectoryFile.h
@@ -26,8 +26,6 @@
 #include "TDatime.h"
 #include "TList.h"
 
-class TList;
-class TBrowser;
 class TKey;
 class TFile;
 
diff --git a/io/io/inc/TFileMerger.h b/io/io/inc/TFileMerger.h
index 339881a42d164..f37121af1711b 100644
--- a/io/io/inc/TFileMerger.h
+++ b/io/io/inc/TFileMerger.h
@@ -12,14 +12,11 @@
 #ifndef ROOT_TFileMerger
 #define ROOT_TFileMerger
 
-#include "TList.h"
 #include "TObject.h"
+#include "TList.h"
 #include "TString.h"
 #include "TStopwatch.h"
 
-#include <memory>
-
-class TList;
 class TFile;
 class TDirectory;
 
diff --git a/io/io/inc/TFilePrefetch.h b/io/io/inc/TFilePrefetch.h
index 6c569767d2fe5..b6b301bf7c298 100644
--- a/io/io/inc/TFilePrefetch.h
+++ b/io/io/inc/TFilePrefetch.h
@@ -12,18 +12,23 @@
 #ifndef ROOT_TFilePrefetch
 #define ROOT_TFilePrefetch
 
-#include "TFile.h"
-#include "TThread.h"
-#include "TFPBlock.h"
-#include "TSemaphore.h"
 #include "TObject.h"
 #include "TString.h"
 #include "TStopwatch.h"
+#include "TThread.h"
+#include "TFile.h"
 
 #include <atomic>
 #include <condition_variable>
 #include <mutex>
 
+#ifdef R__LESS_INCLUDES
+class TSemaphore;
+class TFPBlock;
+#else
+#include "TSemaphore.h"
+#include "TFPBlock.h"
+#endif
 
 class TFilePrefetch : public TObject {
 
diff --git a/io/io/inc/TStreamerInfo.h b/io/io/inc/TStreamerInfo.h
index 67377ed0f60b8..e4ec8d84e273b 100644
--- a/io/io/inc/TStreamerInfo.h
+++ b/io/io/inc/TStreamerInfo.h
@@ -16,13 +16,10 @@
 
 #include "TVirtualStreamerInfo.h"
 
-#include "ThreadLocalStorage.h"
-
 #include "TVirtualCollectionProxy.h"
 
 #include "TObjArray.h"
 
-
 /**
 \class TStreamerInfo
 \ingroup IO
diff --git a/io/io/src/TFile.cxx b/io/io/src/TFile.cxx
index 9b639e951935e..eba02ba3f9075 100644
--- a/io/io/src/TFile.cxx
+++ b/io/io/src/TFile.cxx
@@ -123,6 +123,7 @@ The structure of a directory is shown in TDirectoryFile::TDirectoryFile
 #include "TEnv.h"
 #include "TVirtualMonitoring.h"
 #include "TVirtualMutex.h"
+#include "TMap.h"
 #include "TMathBase.h"
 #include "TObjString.h"
 #include "TStopwatch.h"
diff --git a/io/io/src/TFilePrefetch.cxx b/io/io/src/TFilePrefetch.cxx
index e94ee48f0bc95..ea33089e42d07 100644
--- a/io/io/src/TFilePrefetch.cxx
+++ b/io/io/src/TFilePrefetch.cxx
@@ -15,6 +15,8 @@
 #include "TMD5.h"
 #include "TVirtualPerfStats.h"
 #include "TVirtualMonitoring.h"
+#include "TSemaphore.h"
+#include "TFPBlock.h"
 
 #include <iostream>
 #include <string>
diff --git a/io/io/src/TMakeProject.cxx b/io/io/src/TMakeProject.cxx
index 9933dc50ac66b..210fc2d9a2df1 100644
--- a/io/io/src/TMakeProject.cxx
+++ b/io/io/src/TMakeProject.cxx
@@ -20,6 +20,7 @@ Helper class implementing the TFile::MakeProject.
 #include "TMakeProject.h"
 #include "TClass.h"
 #include "TClassEdit.h"
+#include "TList.h"
 #include "TROOT.h"
 #include "TMD5.h"
 #include "TStreamerInfo.h"
diff --git a/io/io/src/TStreamerInfoReadBuffer.cxx b/io/io/src/TStreamerInfoReadBuffer.cxx
index 68ce0948f4064..e9054d8d4e26e 100644
--- a/io/io/src/TStreamerInfoReadBuffer.cxx
+++ b/io/io/src/TStreamerInfoReadBuffer.cxx
@@ -24,6 +24,7 @@
 #include "TContainerConverters.h"
 #include "TVirtualArray.h"
 #include "TVirtualObject.h"
+#include "ThreadLocalStorage.h"
 
 // GetCurrentElement.
 // Currently only used by TRef::Streamer.
diff --git a/io/mpi/src/TMPIFile.cxx b/io/mpi/src/TMPIFile.cxx
index cf81e36097fd5..e322a004521e5 100644
--- a/io/mpi/src/TMPIFile.cxx
+++ b/io/mpi/src/TMPIFile.cxx
@@ -12,6 +12,7 @@
 #include "TMPIFile.h"
 #include "TFileCacheWrite.h"
 #include "TKey.h"
+#include "THashTable.h"
 #include "TMath.h"
 
 ClassImp(TMPIFile);
diff --git a/io/rootpcm/src/rootclingIO.cxx b/io/rootpcm/src/rootclingIO.cxx
index fae4eaaed259e..f9cf38a829c83 100644
--- a/io/rootpcm/src/rootclingIO.cxx
+++ b/io/rootpcm/src/rootclingIO.cxx
@@ -17,6 +17,7 @@
 #include "TError.h"
 #include "TFile.h"
 #include "TProtoClass.h"
+#include "TDataMember.h"
 #include "TROOT.h"
 #include "TStreamerInfo.h"
 #include "TClassEdit.h"
diff --git a/io/sql/inc/TBufferSQL2.h b/io/sql/inc/TBufferSQL2.h
index 51b11b5709c68..ce6c630f8b686 100644
--- a/io/sql/inc/TBufferSQL2.h
+++ b/io/sql/inc/TBufferSQL2.h
@@ -6,7 +6,6 @@
 
 #include "TBufferText.h"
 #include "TString.h"
-#include "TObjArray.h"
 
 class TMap;
 class TExMap;
diff --git a/io/xml/inc/TXMLPlayer.h b/io/xml/inc/TXMLPlayer.h
index 5a6a2e5ab1008..6cb268c7adf0b 100644
--- a/io/xml/inc/TXMLPlayer.h
+++ b/io/xml/inc/TXMLPlayer.h
@@ -14,14 +14,13 @@
 
 #include "TObject.h"
 
-#include "TList.h"
-
 #include "TXMLSetup.h"
 
 class TStreamerInfo;
 class TStreamerElement;
 class TStreamerSTL;
 class TDataMember;
+class TList;
 
 class TXMLPlayer : public TObject {
 public:
diff --git a/io/xml/src/TXMLPlayer.cxx b/io/xml/src/TXMLPlayer.cxx
index ca5d59f91635e..d2290ff9a5d79 100644
--- a/io/xml/src/TXMLPlayer.cxx
+++ b/io/xml/src/TXMLPlayer.cxx
@@ -105,6 +105,7 @@
 
 #include "Riostream.h"
 #include "TROOT.h"
+#include "TList.h"
 #include "TClass.h"
 #include "TVirtualStreamerInfo.h"
 #include "TStreamerElement.h"
diff --git a/io/xml/src/TXMLSetup.cxx b/io/xml/src/TXMLSetup.cxx
index e3f28660345fc..a3ad64b8944e9 100644
--- a/io/xml/src/TXMLSetup.cxx
+++ b/io/xml/src/TXMLSetup.cxx
@@ -33,6 +33,7 @@
 #include "TXMLSetup.h"
 
 #include "TROOT.h"
+#include "TList.h"
 #include "TClass.h"
 #include "TStreamerElement.h"
 
diff --git a/main/src/h2root.cxx b/main/src/h2root.cxx
index 271b7d9bfe353..548b3e7c4233b 100644
--- a/main/src/h2root.cxx
+++ b/main/src/h2root.cxx
@@ -27,6 +27,7 @@
 #include "TFile.h"
 #include "TDirectoryFile.h"
 #include "TTree.h"
+#include "TBranch.h"
 #include "TLeafI.h"
 #include "TH1.h"
 #include "TH2.h"
diff --git a/math/foam/src/TFoam.cxx b/math/foam/src/TFoam.cxx
index 3c6c871e2fa01..953e14a34ff49 100644
--- a/math/foam/src/TFoam.cxx
+++ b/math/foam/src/TFoam.cxx
@@ -83,6 +83,7 @@ S. Jadach, Computer Physics Communications 152 (2003) 55.
 #include "TFoamCell.h"
 #include "Riostream.h"
 #include "TH1.h"
+#include "TRefArray.h"
 #include "TObjArray.h"
 #include "TMethodCall.h"
 #include "TRandom.h"
diff --git a/math/fumili/src/TFumili.cxx b/math/fumili/src/TFumili.cxx
index 18443d4091154..764e61fad7a7b 100644
--- a/math/fumili/src/TFumili.cxx
+++ b/math/fumili/src/TFumili.cxx
@@ -107,6 +107,7 @@ function argument.
 #include "TH1.h"
 #include "TMath.h"
 #include "TROOT.h"
+#include "TList.h"
 #include "TVirtualFitter.h"
 
 
diff --git a/math/mathcore/src/TStatistic.cxx b/math/mathcore/src/TStatistic.cxx
index 3a966882c0e67..c2b1c8342df7e 100644
--- a/math/mathcore/src/TStatistic.cxx
+++ b/math/mathcore/src/TStatistic.cxx
@@ -12,6 +12,7 @@
 #include "TStatistic.h"
 
 #include "TROOT.h"
+#include "TList.h"
 
 // clang-format off
 /**
diff --git a/math/mathmore/inc/Math/ChebyshevApprox.h b/math/mathmore/inc/Math/ChebyshevApprox.h
index 3ee79ff8babc5..a663c0f579f6d 100644
--- a/math/mathmore/inc/Math/ChebyshevApprox.h
+++ b/math/mathmore/inc/Math/ChebyshevApprox.h
@@ -46,7 +46,7 @@
 
 #include "Math/GSLFunctionAdapter.h"
 
-#include <memory>
+#include <utility>
 #include <cstddef>
 
 
diff --git a/math/minuit/src/TMinuit.cxx b/math/minuit/src/TMinuit.cxx
index dd31959aecb72..df3e563a73d80 100644
--- a/math/minuit/src/TMinuit.cxx
+++ b/math/minuit/src/TMinuit.cxx
@@ -335,6 +335,7 @@ into account the non-linearities much more precisely.
 #include <stdio.h>
 
 #include "TROOT.h"
+#include "TList.h"
 #include "TMinuit.h"
 #include "TMath.h"
 #include "TError.h"
diff --git a/math/minuit/src/TMinuitMinimizer.cxx b/math/minuit/src/TMinuitMinimizer.cxx
index 608b6beca92d5..9420c51e91e17 100644
--- a/math/minuit/src/TMinuitMinimizer.cxx
+++ b/math/minuit/src/TMinuitMinimizer.cxx
@@ -16,6 +16,7 @@
 
 #include "TMinuit.h"
 #include "TROOT.h"
+#include "TList.h"
 
 #include "TGraph.h" // needed for scan
 #include "TError.h"
diff --git a/net/netxng/src/TNetXNGFileStager.cxx b/net/netxng/src/TNetXNGFileStager.cxx
index 52bf699f9a275..d01c7f1eb2b9b 100644
--- a/net/netxng/src/TNetXNGFileStager.cxx
+++ b/net/netxng/src/TNetXNGFileStager.cxx
@@ -22,6 +22,7 @@
 #include "TNetXNGSystem.h"
 #include "THashList.h"
 #include "TFileInfo.h"
+#include "TUrl.h"
 #include "TFileCollection.h"
 #include <XrdCl/XrdClFileSystem.hh>
 
diff --git a/proof/proof/src/TProofQueryResult.cxx b/proof/proof/src/TProofQueryResult.cxx
index 9d5e4ef02b188..fa1e3e9f91d54 100644
--- a/proof/proof/src/TProofQueryResult.cxx
+++ b/proof/proof/src/TProofQueryResult.cxx
@@ -21,7 +21,7 @@ TQueryResult version adapted to PROOF neeeds
 #include "TList.h"
 #include "TProofQueryResult.h"
 #include "TSystem.h"
-
+#include "TMacro.h"
 
 ClassImp(TProofQueryResult);
 
diff --git a/proof/proofbench/src/TProofBench.cxx b/proof/proofbench/src/TProofBench.cxx
index e69466553f754..3efcb00389739 100644
--- a/proof/proofbench/src/TProofBench.cxx
+++ b/proof/proofbench/src/TProofBench.cxx
@@ -38,6 +38,7 @@
 #include "TFileInfo.h"
 #include "THashList.h"
 #include "TKey.h"
+#include "TMap.h"
 #include "TObjString.h"
 #include "TProof.h"
 #include "TROOT.h"
diff --git a/proof/proofplayer/src/TProofMonSenderML.cxx b/proof/proofplayer/src/TProofMonSenderML.cxx
index f3b11e0b9137b..e6fc9cb0f006e 100644
--- a/proof/proofplayer/src/TProofMonSenderML.cxx
+++ b/proof/proofplayer/src/TProofMonSenderML.cxx
@@ -27,6 +27,7 @@ TProofMonSender implementation for the ML writer
 #include "TPluginManager.h"
 #include "TProofDebug.h"
 #include "TROOT.h"
+#include "TUrl.h"
 #include "TSystem.h"
 #include "TObjString.h"
 #include "TVirtualMonitoring.h"
diff --git a/proof/proofplayer/src/TProofMonSenderSQL.cxx b/proof/proofplayer/src/TProofMonSenderSQL.cxx
index 1cc0f671596d9..90605f6a79799 100644
--- a/proof/proofplayer/src/TProofMonSenderSQL.cxx
+++ b/proof/proofplayer/src/TProofMonSenderSQL.cxx
@@ -23,6 +23,7 @@ TProofMonSender implementation for the SQL writers
 #include "TFileInfo.h"
 #include "THashList.h"
 #include "TList.h"
+#include "TUrl.h"
 #include "TPluginManager.h"
 #include "TProofDebug.h"
 #include "TROOT.h"
diff --git a/test/stressGUI.cxx b/test/stressGUI.cxx
index f1590679a33ec..de746abdf8dc3 100644
--- a/test/stressGUI.cxx
+++ b/test/stressGUI.cxx
@@ -68,6 +68,7 @@
 #include <TGImageMap.h>
 #include <TASPaletteEditor.h>
 #include <TControlBar.h>
+#include <TControlBarImp.h>
 #include <TGSpeedo.h>
 #include <TGShapedFrame.h>
 #include <TGSplitFrame.h>
diff --git a/tmva/tmva/src/Classification.cxx b/tmva/tmva/src/Classification.cxx
index e8e28819242ee..9aa0e8b93b214 100644
--- a/tmva/tmva/src/Classification.cxx
+++ b/tmva/tmva/src/Classification.cxx
@@ -29,9 +29,11 @@
 
 #include <TROOT.h>
 #include <TFile.h>
+#include <TKey.h>
 #include <TTree.h>
 #include <TKey.h>
 #include <TLeaf.h>
+#include <TBranch.h>
 #include <TEventList.h>
 #include <TH2.h>
 #include <TText.h>
diff --git a/tmva/tmva/src/DataSetFactory.cxx b/tmva/tmva/src/DataSetFactory.cxx
index 30fa9028cafcf..5ae6999774b51 100644
--- a/tmva/tmva/src/DataSetFactory.cxx
+++ b/tmva/tmva/src/DataSetFactory.cxx
@@ -57,6 +57,7 @@ Class that contains all the data information
 #include "TVectorF.h"
 #include "TMath.h"
 #include "TROOT.h"
+#include "TBranch.h"
 
 #include "TMVA/MsgLogger.h"
 #include "TMVA/Configurable.h"
diff --git a/tmva/tmva/src/PDF.cxx b/tmva/tmva/src/PDF.cxx
index eaa52811f75e2..b0e6e59601089 100644
--- a/tmva/tmva/src/PDF.cxx
+++ b/tmva/tmva/src/PDF.cxx
@@ -51,6 +51,7 @@ PDF wrapper for histograms; uses user-defined spline interpolation.
 #include "TH1F.h"
 #include "TMath.h"
 #include "TVectorD.h"
+#include "TGraph.h"
 
 #include <cstdlib>
 #include <iomanip>
diff --git a/tmva/tmva/src/ROCCalc.cxx b/tmva/tmva/src/ROCCalc.cxx
index 52268fc81901d..1472e371bbc39 100644
--- a/tmva/tmva/src/ROCCalc.cxx
+++ b/tmva/tmva/src/ROCCalc.cxx
@@ -23,9 +23,9 @@
 #include "TXMLEngine.h"
 #include "TROOT.h"
 #include "TColor.h"
-#include "TMVA/Config.h"
-
+#include "TGraph.h"
 
+#include "TMVA/Config.h"
 #include "TMVA/Tools.h"
 #include "TMVA/ROCCalc.h"
 #include "TMVA/Event.h"
diff --git a/tree/tree/inc/ROOT/TIOFeatures.hxx b/tree/tree/inc/ROOT/TIOFeatures.hxx
index 41685df813ffd..11e0c54d5d6a6 100644
--- a/tree/tree/inc/ROOT/TIOFeatures.hxx
+++ b/tree/tree/inc/ROOT/TIOFeatures.hxx
@@ -17,7 +17,7 @@ class TBasket;
 class TBranch;
 class TTree;
 
-// keep it here to have a note that was removed  
+// keep it here to have a note that was removed
 // #ifndef R__LESS_INCLUDES
 // #include "TBasket.h"
 // #include <memory>
diff --git a/tree/tree/inc/TBranch.h b/tree/tree/inc/TBranch.h
index 351096d387c77..c160023f1f564 100644
--- a/tree/tree/inc/TBranch.h
+++ b/tree/tree/inc/TBranch.h
@@ -23,14 +23,12 @@
 //     the list of TLeaves (branch description)                         //
 //////////////////////////////////////////////////////////////////////////
 
-#include <memory>
-
-#include "Compression.h"
+#include "TNamed.h"
 #include "TAttFill.h"
+#include "TObjArray.h"
 #include "TBranchCacheInfo.h"
 #include "TDataType.h"
-#include "TNamed.h"
-#include "TObjArray.h"
+#include "Compression.h"
 #include "ROOT/TIOFeatures.hxx"
 
 class TTree;
diff --git a/tree/tree/inc/TBranchElement.h b/tree/tree/inc/TBranchElement.h
index 38c19915022bb..58448a10b6ad9 100644
--- a/tree/tree/inc/TBranchElement.h
+++ b/tree/tree/inc/TBranchElement.h
@@ -27,8 +27,6 @@
 
 #include "TTree.h"
 
-#include "TError.h"
-
 class TFolder;
 class TStreamerInfo;
 class TVirtualCollectionProxy;
diff --git a/tree/tree/inc/TBranchRef.h b/tree/tree/inc/TBranchRef.h
index 0fa045829a399..246f525601148 100644
--- a/tree/tree/inc/TBranchRef.h
+++ b/tree/tree/inc/TBranchRef.h
@@ -22,7 +22,12 @@
 
 
 #include "TBranch.h"
+
+#ifdef R__LESS_INCLUDES
+class TRefTable;
+#else
 #include "TRefTable.h"
+#endif
 
 class TTree;
 
diff --git a/tree/tree/inc/TChain.h b/tree/tree/inc/TChain.h
index b17963e1503e9..0da5708dca84b 100644
--- a/tree/tree/inc/TChain.h
+++ b/tree/tree/inc/TChain.h
@@ -22,7 +22,6 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TTree.h"
-#include <iosfwd>
 
 class TFile;
 class TBrowser;
diff --git a/tree/tree/inc/TLeaf.h b/tree/tree/inc/TLeaf.h
index 9490eb635e2bb..6440c95f4a46a 100644
--- a/tree/tree/inc/TLeaf.h
+++ b/tree/tree/inc/TLeaf.h
@@ -41,7 +41,13 @@
 //////////////////////////////////////////////////////////////////////////
 
 
+#include "TNamed.h"
+
+#ifdef R__LESS_INCLUDES
+class TBranch;
+#else
 #include "TBranch.h"
+#endif
 
 class TClonesArray;
 class TBrowser;
diff --git a/tree/tree/inc/TLeafD32.h b/tree/tree/inc/TLeafD32.h
index 48d0196d22b50..ff2378141dd35 100644
--- a/tree/tree/inc/TLeafD32.h
+++ b/tree/tree/inc/TLeafD32.h
@@ -20,9 +20,11 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TStreamerElement.h"
 #include "TLeaf.h"
 
+class TStreamerElement;
+
+
 class TLeafD32 : public TLeaf {
 
 protected:
diff --git a/tree/tree/inc/TLeafF16.h b/tree/tree/inc/TLeafF16.h
index 8a9137df19429..5a25256b6209b 100644
--- a/tree/tree/inc/TLeafF16.h
+++ b/tree/tree/inc/TLeafF16.h
@@ -20,9 +20,10 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TStreamerElement.h"
 #include "TLeaf.h"
 
+class TStreamerElement;
+
 class TLeafF16 : public TLeaf {
 
 protected:
diff --git a/tree/tree/inc/TQueryResult.h b/tree/tree/inc/TQueryResult.h
index b2de35ab753f7..30e007949d12e 100644
--- a/tree/tree/inc/TQueryResult.h
+++ b/tree/tree/inc/TQueryResult.h
@@ -23,9 +23,14 @@
 
 #include "TNamed.h"
 #include "TDatime.h"
-#include "TMacro.h"
 #include "TString.h"
 
+#ifdef R__LESS_INCLUDES
+class TMacro;
+#else
+#include "TMacro.h"
+#endif
+
 class TBrowser;
 class TTreePlayer;
 class TQueryResult;
diff --git a/tree/tree/inc/TSelector.h b/tree/tree/inc/TSelector.h
index 05fd1387e1e5c..aee3a8a2c53f7 100644
--- a/tree/tree/inc/TSelector.h
+++ b/tree/tree/inc/TSelector.h
@@ -26,10 +26,8 @@
 #include "TString.h"
 #include "TSelectorList.h"
 
-
 class TTree;
 
-
 class TSelector : public TObject {
 
 public:
diff --git a/tree/tree/inc/TTreeCache.h b/tree/tree/inc/TTreeCache.h
index f29dbb23e9faf..243792c9aaffd 100644
--- a/tree/tree/inc/TTreeCache.h
+++ b/tree/tree/inc/TTreeCache.h
@@ -23,9 +23,6 @@
 
 #include "TFileCacheRead.h"
 
-#include <cstdint>
-#include <memory>
-#include <utility>
 #include <vector>
 
 class TTree;
diff --git a/tree/tree/src/TBranchBrowsable.cxx b/tree/tree/src/TBranchBrowsable.cxx
index b72ea22fa217a..4ebf05a91018b 100644
--- a/tree/tree/src/TBranchBrowsable.cxx
+++ b/tree/tree/src/TBranchBrowsable.cxx
@@ -25,6 +25,7 @@
 #include "TStreamerElement.h"
 #include "TVirtualCollectionProxy.h"
 #include "TRef.h"
+#include "TError.h"
 #include <algorithm>
 
 ClassImp(TVirtualBranchBrowsable);
diff --git a/tree/tree/src/TBranchRef.cxx b/tree/tree/src/TBranchRef.cxx
index ecce2836b7e92..ad17f34b4dc8d 100644
--- a/tree/tree/src/TBranchRef.cxx
+++ b/tree/tree/src/TBranchRef.cxx
@@ -32,9 +32,9 @@ TObjArray.
 */
 
 #include "TBranchRef.h"
-#include "TBuffer.h"
 #include "TTree.h"
 #include "TBasket.h"
+#include "TRefTable.h"
 #include "TFile.h"
 #include "TFriendElement.h"
 
diff --git a/tree/tree/src/TChain.cxx b/tree/tree/src/TChain.cxx
index 5ff3533a7b512..a984eb98638b6 100644
--- a/tree/tree/src/TChain.cxx
+++ b/tree/tree/src/TChain.cxx
@@ -46,6 +46,7 @@ the trees in the chain.
 #include "TPluginManager.h"
 #include "TROOT.h"
 #include "TRegexp.h"
+#include "Riostream.h"
 #include "TSelector.h"
 #include "TSystem.h"
 #include "TTree.h"
diff --git a/tree/tree/src/TLeafD32.cxx b/tree/tree/src/TLeafD32.cxx
index 7cff811964c79..e2944a78d7667 100644
--- a/tree/tree/src/TLeafD32.cxx
+++ b/tree/tree/src/TLeafD32.cxx
@@ -19,6 +19,7 @@ A TLeaf for a 24 bit truncated floating point data type.
 #include "TBranch.h"
 #include "TBuffer.h"
 #include "TClonesArray.h"
+#include "TStreamerElement.h"
 #include "Riostream.h"
 
 ClassImp(TLeafD32);
diff --git a/tree/tree/src/TLeafF16.cxx b/tree/tree/src/TLeafF16.cxx
index 922cae97c4d27..356d95627680b 100644
--- a/tree/tree/src/TLeafF16.cxx
+++ b/tree/tree/src/TLeafF16.cxx
@@ -19,6 +19,7 @@ A TLeaf for a 24 bit truncated floating point data type.
 #include "TBranch.h"
 #include "TBuffer.h"
 #include "TClonesArray.h"
+#include "TStreamerElement.h"
 #include "Riostream.h"
 
 ClassImp(TLeafF16);
diff --git a/tree/tree/src/TQueryResult.cxx b/tree/tree/src/TQueryResult.cxx
index 3400ad99a033d..fe68a8b4db799 100644
--- a/tree/tree/src/TQueryResult.cxx
+++ b/tree/tree/src/TQueryResult.cxx
@@ -18,11 +18,11 @@ A container class for query results.
 #include <string.h>
 
 #include "TBrowser.h"
-#include "TError.h"
 #include "TEventList.h"
 #include "TQueryResult.h"
 #include "TRegexp.h"
 #include "TROOT.h"
+#include "TMacro.h"
 #include "TMath.h"
 #include "TSelector.h"
 #include "TSystem.h"
diff --git a/tree/tree/src/TTree.cxx b/tree/tree/src/TTree.cxx
index dcc1d0a59e9bf..50a6bc8f7e5ff 100644
--- a/tree/tree/src/TTree.cxx
+++ b/tree/tree/src/TTree.cxx
@@ -395,6 +395,7 @@ End_Macro
 #include "TROOT.h"
 #include "TRealData.h"
 #include "TRegexp.h"
+#include "TRefTable.h"
 #include "TStreamerElement.h"
 #include "TStreamerInfo.h"
 #include "TStyle.h"
diff --git a/tree/tree/src/TTreeCacheUnzip.cxx b/tree/tree/src/TTreeCacheUnzip.cxx
index 39cc5c01295aa..cd0ea1514d0e1 100644
--- a/tree/tree/src/TTreeCacheUnzip.cxx
+++ b/tree/tree/src/TTreeCacheUnzip.cxx
@@ -25,6 +25,7 @@ A TTreeCache which exploits parallelized decompression of its own content.
 #include "TEventList.h"
 #include "TFile.h"
 #include "TMath.h"
+#include "TROOT.h"
 #include "TMutex.h"
 #include "ROOT/RMakeUnique.hxx"
 
diff --git a/tree/tree/test/TIOFeatures.cxx b/tree/tree/test/TIOFeatures.cxx
index 2874e614f0ba5..0c50531efe96b 100644
--- a/tree/tree/test/TIOFeatures.cxx
+++ b/tree/tree/test/TIOFeatures.cxx
@@ -6,6 +6,7 @@
 #include "gtest/gtest.h"
 
 #include <vector>
+#include "TBasket.h"
 
 TEST(TIOFeatures, IOBits)
 {
diff --git a/tree/treeplayer/src/TTreeFormula.cxx b/tree/treeplayer/src/TTreeFormula.cxx
index 64b1a0353e8ea..e05d0b921ef99 100644
--- a/tree/treeplayer/src/TTreeFormula.cxx
+++ b/tree/treeplayer/src/TTreeFormula.cxx
@@ -11,6 +11,7 @@
 
 #include "TROOT.h"
 #include "TTreeFormula.h"
+#include "TList.h"
 #include "TTree.h"
 #include "TBuffer.h"
 #include "TBranch.h"
diff --git a/tree/treeplayer/src/TTreeGeneratorBase.cxx b/tree/treeplayer/src/TTreeGeneratorBase.cxx
index e2b1658e1d6d2..edbd89c3c306f 100644
--- a/tree/treeplayer/src/TTreeGeneratorBase.cxx
+++ b/tree/treeplayer/src/TTreeGeneratorBase.cxx
@@ -20,6 +20,7 @@
 #include "TStreamerElement.h"
 #include "TStreamerInfo.h"
 #include "TTree.h"
+#include "TError.h"
 #include "TVirtualCollectionProxy.h"
 #include "TVirtualStreamerInfo.h"
 
diff --git a/tree/treeplayer/src/TTreePlayer.cxx b/tree/treeplayer/src/TTreePlayer.cxx
index aa22f5edbb734..89d91b158d74d 100644
--- a/tree/treeplayer/src/TTreePlayer.cxx
+++ b/tree/treeplayer/src/TTreePlayer.cxx
@@ -76,6 +76,7 @@ extra libraries (Histogram, display, etc).
 #include "TVirtualMonitoring.h"
 #include "TTreeCache.h"
 #include "TVirtualMutex.h"
+#include "ThreadLocalStorage.h"
 
 #include "HFitInterface.h"
 #include "Fit/BinData.h"
diff --git a/tree/treeplayer/src/TTreeReaderArray.cxx b/tree/treeplayer/src/TTreeReaderArray.cxx
index 5101c01121a99..508e8ad91fdac 100644
--- a/tree/treeplayer/src/TTreeReaderArray.cxx
+++ b/tree/treeplayer/src/TTreeReaderArray.cxx
@@ -21,6 +21,7 @@
 #include "TFriendElement.h"
 #include "TFriendProxy.h"
 #include "TLeaf.h"
+#include "TList.h"
 #include "TROOT.h"
 #include "TStreamerInfo.h"
 #include "TStreamerElement.h"
diff --git a/tree/treeviewer/src/TSpider.cxx b/tree/treeviewer/src/TSpider.cxx
index b4eac1b50f104..039483741b135 100644
--- a/tree/treeviewer/src/TSpider.cxx
+++ b/tree/treeviewer/src/TSpider.cxx
@@ -16,6 +16,7 @@
 #include "TGraphPolargram.h"
 #include "TPolyLine.h"
 #include "TNtuple.h"
+#include "TBranch.h"
 #include "TTreeFormula.h"
 #include "TTreeFormulaManager.h"
 #include "TList.h"
diff --git a/tree/treeviewer/src/TTreeViewer.cxx b/tree/treeviewer/src/TTreeViewer.cxx
index b846acd0c4d7e..83e5b06968aec 100644
--- a/tree/treeviewer/src/TTreeViewer.cxx
+++ b/tree/treeviewer/src/TTreeViewer.cxx
@@ -190,6 +190,7 @@ or :
 #include "TContextMenu.h"
 #include "TInterpreter.h"
 #include "TLeaf.h"
+#include "TBranch.h"
 #include "TRootHelpDialog.h"
 #include "TSystem.h"
 #include "TApplication.h"