diff --git a/Makefile.fetch b/Makefile.fetch
index cdac3ae76b1d..46bbc3624723 100644
--- a/Makefile.fetch
+++ b/Makefile.fetch
@@ -53,6 +53,7 @@ endef
 
 # fetch_Download_item url variable-name
 define fetch_Download_item
+$(if $(strip $($(2))),,$(error fetch__Download_item: $(2) is empty))
 $(if $(filter undefined,$(origin $(subst _TARBALL,_MD5SUM,$(subst _PACK,_MD5SUM,$(2))))),\
 	$(if $(call fetch_Download__is_checksum,$(firstword $(subst -, ,$($(2))))),\
 		$(call fetch__Download_item,$1,$($2),$(firstword $(subst -, ,$($(2))))),\