diff --git a/Makefile b/Makefile
index 4063ee2d4031..0b68f6a5d343 100644
--- a/Makefile
+++ b/Makefile
@@ -917,10 +917,10 @@ endif
 
 ifdef CONFIG_LTO_CLANG
 ifdef CONFIG_LTO_CLANG_THIN
-CC_FLAGS_LTO	+= -flto=thin -fsplit-lto-unit
+CC_FLAGS_LTO	:= -flto=thin -fsplit-lto-unit
 KBUILD_LDFLAGS	+= --thinlto-cache-dir=$(extmod-prefix).thinlto-cache
 else
-CC_FLAGS_LTO	+= -flto
+CC_FLAGS_LTO	:= -flto
 endif
 
 ifeq ($(SRCARCH),x86)