diff --git a/Makefile b/Makefile
index ed081e3..87d659d 100644
--- a/Makefile
+++ b/Makefile
@@ -946,7 +946,7 @@
 KBUILD_CFLAGS   += $(call cc-option,-Werror=designated-init)
 
 # change __FILE__ to the relative path from the srctree
-KBUILD_CFLAGS	+= $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
+KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
 
 # ensure -fcf-protection is disabled when using retpoline as it is
 # incompatible with -mindirect-branch=thunk-extern