diff --git a/Makefile b/Makefile
index 46967152919..09748e5908a 100644
--- a/Makefile
+++ b/Makefile
@@ -58,7 +58,7 @@ build_tags += $(BUILD_TAGS)
 build_tags := $(strip $(build_tags))
 
 whitespace :=
-whitespace += $(whitespace)
+whitespace := $(whitespace) $(whitespace)
 comma := ,
 build_tags_comma_sep := $(subst $(whitespace),$(comma),$(build_tags))