diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3e8f903c60a64dcd652528c229fd52fdbdbbfd17..f0a789677effe0f53cb3965371a0b48f1c3c9f9d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -150,8 +150,11 @@ get_property(__clingetcpch GLOBAL PROPERTY CLINGETCPCH)
 
 string(REGEX REPLACE "[ ]-" ";-" CMAKE_CXX_FLAGS_SEPARATE ${CMAKE_CXX_FLAGS})
 if(cxxmodules)
-  # rootcling doesn't know what to do with these flags.
-  # FIXME: Disable until until somebody teaches it.
+  # rootcling uses our internal version of clang. Passing the modules flags here
+  # would allow rootcling to find module files built by the external compiler
+  # (eg. $CXX or $CC). This, in turn, would cause problems if we are using
+  # different clang version (even different commit revision) as the modules files
+  # are not guaranteed to be compatible among clang revisions.
   string(REPLACE "${ROOT_CXXMODULES_FLAGS}" "" CMAKE_CXX_FLAGS_SEPARATE ${CMAKE_CXX_FLAGS_SEPARATE})
 endif(cxxmodules)
 add_custom_command(OUTPUT etc/dictpch/allLinkDefs.h
diff --git a/Makefile b/Makefile
index 29278e9d35e0a181f221c8c870841ec76cf72791..592a2fb1e9bba9a6f12fa0325d571798f5d32bb7 100644
--- a/Makefile
+++ b/Makefile
@@ -1137,8 +1137,11 @@ changelog:
 releasenotes:
 	@$(MAKERELNOTES)
 ROOTCLING_CXXFLAGS := $(CXXFLAGS)
-# rootcling doesn't know what to do with these flags.
-# FIXME: Disable until until somebody teaches it.
+# rootcling uses our internal version of clang. Passing the modules flags here
+# would allow rootcling to find module files built by the external compiler
+# (eg. $CXX or $CC). This, in turn, would cause problems if we are using
+# different clang version (even different commit revision) as the modules files
+# are not guaranteed to be compatible among clang revisions.
 ifeq ($(CXXMODULES),yes)
 ROOTCLING_CXXFLAGS := $(filter-out $(ROOT_CXXMODULES_CXXFLAGS),$(CXXFLAGS))
 endif