diff --git a/core/metacling/src/TCling.cxx b/core/metacling/src/TCling.cxx
index d6b35d42f0879..ad9262a6f6dc7 100644
--- a/core/metacling/src/TCling.cxx
+++ b/core/metacling/src/TCling.cxx
@@ -1176,8 +1176,6 @@ TCling::TCling(const char *name, const char *title, const char* const argv[])
 #ifdef R__USE_CXXMODULES
    useCxxModules = true;
 #endif
-   if (useCxxModules)
-     fHeaderParsingOnDemand = false;
 
    llvm::install_fatal_error_handler(&exceptionErrorHandler);
 
@@ -1755,6 +1753,10 @@ void TCling::RegisterModule(const char* modulename,
    // I/O; see rootcling.cxx after the call to TCling__GetInterpreter().
    if (fromRootCling) return;
 
+   // When we cannot provide a module for the library we should enable header
+   // parsing. This 'mixed' mode ensures gradual migration to modules.
+   fHeaderParsingOnDemand = !hasCxxModule;
+
    // Treat Aclic Libs in a special way. Do not delay the parsing.
    bool hasHeaderParsingOnDemand = fHeaderParsingOnDemand;
    bool isACLiC = strstr(modulename, "_ACLiC_dict") != nullptr;