diff --git a/make/Makefile b/make/Makefile
index b0e0de9b..913d9978 100644
--- a/make/Makefile
+++ b/make/Makefile
@@ -27,5 +27,5 @@ cache-projects: $(CACHE_PROJECTS_MK)
 clean-cache-projects:
 	rm -f $(CACHE_PROJECTS_MK)
 $(CACHE_PROJECTS_MK): $(CACHE_PROJECT_MK)
-	sed '/\($(subst $(space),\|,$(CACHED_VARS_ONLY_PROJECT))\)\s*[:?]\?=/ d' $< > $@.tmp
+	sed -E '/^[[:blank:]]*ifndef[[:blank:]]+($(subst $(space),|,$(CACHED_VARS_ONLY_PROJECT)))[[:blank:]]*$$/,/^[[:blank:]]*endif[[:blank:]]*$$/d' $< > $@.tmp
 	mv $@.tmp $@