diff --git a/pkg/package.mk b/pkg/package.mk
index d55c8fee9..79af74f06 100644
--- a/pkg/package.mk
+++ b/pkg/package.mk
@@ -7,16 +7,16 @@ HASH_COMMIT?=HEAD # Setting this is only really useful with the show-tag target
 HASH?=$(shell git ls-tree --full-tree $(HASH_COMMIT) -- $(CURDIR) | awk '{print $$3}')
 
 ifneq ($(HASH_COMMIT),HEAD) # Others can't be dirty by definition
-DIRTY=$(shell git update-index -q --refresh && git diff-index --quiet HEAD -- $(CURDIR) || echo "-dirty")
+DIRTY:=$(shell git update-index -q --refresh && git diff-index --quiet HEAD -- $(CURDIR) || echo "-dirty")
 endif
 endif
 
-TAG=$(ORG)/$(IMAGE):$(HASH)$(DIRTY)
+TAG:=$(ORG)/$(IMAGE):$(HASH)$(DIRTY)
 
 BASE_DEPS=Dockerfile Makefile
 
 # Get a release tag, if present
-RELEASE=$(shell git tag -l --points-at HEAD)
+RELEASE:=$(shell git tag -l --points-at HEAD)
 
 ifdef NETWORK
 NET_OPT=