diff --git a/core/metacling/src/TCling.cxx b/core/metacling/src/TCling.cxx
index b1478709df238..6659294ea68c6 100644
--- a/core/metacling/src/TCling.cxx
+++ b/core/metacling/src/TCling.cxx
@@ -1159,6 +1159,7 @@ static void LoadCoreModules(cling::Interpreter &interp)
    // them. This will be wrapped into an `import` declaration by clang, so we
    // only make those modules available, not actually textually include those
    // headers.
+   // FIXME: Use clang::ASTReader::makeModuleVisible.
    std::stringstream declarations;
    for (StringRef H : moduleHeaders) {
       declarations << "#include \"" << H.str() << "\"\n";
diff --git a/interpreter/cling/lib/Interpreter/CIFactory.cpp b/interpreter/cling/lib/Interpreter/CIFactory.cpp
index ec754393c9f9a..15e466cc2d269 100644
--- a/interpreter/cling/lib/Interpreter/CIFactory.cpp
+++ b/interpreter/cling/lib/Interpreter/CIFactory.cpp
@@ -825,7 +825,16 @@ static void stringifyPreprocSetting(PreprocessorOptions& PPOpts,
       // is a ROOT-specific issue tracked by ROOT-9088.
       // FIXME: Remove after merging ROOT's PR1306.
       argvCompile.push_back("-Wno-modules-import-nested-redundant");
-
+      // FIXME: We get an error "'cling/module.modulemap' from the precompiled
+      //  header has been overridden". This comes from a bug that rootcling
+      // introduces by adding a lot of garbage in the PCH/PCM files because it
+      // essentially serializes its current state of the AST. That usually
+      // includes a few memory buffers which override their own contents.
+      // We know how to remove this: just implement a callback in clang
+      // which calls back the interpreter when a module file is built. This is
+      // a lot of work as it needs fixing rootcling. See RE-0003.
+      argvCompile.push_back("-Xclang");
+      argvCompile.push_back("-fno-validate-pch");
     }
 
     if (!COpts.Language) {