diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -138,6 +138,9 @@
       BOOL "Whether to build ${upper_proj} as part of LLVM" FORCE
     )
   endforeach()
+  if ("clang-tools-extra" IN_LIST LLVM_ENABLE_PROJECTS AND NOT "clang" IN_LIST LLVM_ENABLE_PROJECTS)
+    message(WARNING "'clang-tools-extra' is enabled, yet it depends on 'clang' which is disabled")
+  endif()
 endif()
 unset(SHOULD_ENABLE_PROJECT)