diff --git a/Makefile b/Makefile
index e59441c4329..6ea55336b7a 100644
--- a/Makefile
+++ b/Makefile
@@ -77,6 +77,7 @@ ifeq ($(MAKECMDGOALS),install-clang)
 endif
 
 ifeq ($(MAKECMDGOALS),clang-only)
+  BUILD_CLANG_ONLY := YES
   DIRS := $(filter-out tools docs unittests, $(DIRS)) \
           tools/clang tools/lto
   OPTIONAL_DIRS :=