diff --git a/Makefile b/Makefile
index ba15fda..03bbf86 100644
--- a/Makefile
+++ b/Makefile
@@ -51,6 +51,7 @@ docker_main:
 	${DOCKER_BUILD_MAIN_CMD}
 
 docker_tag:
+	test ${TAG}
 	${DOCKER_BUILD_TAG_CMD}
 
 #Everything right of the pipe is order-only prerequisites.