diff --git a/pkg/package.mk b/pkg/package.mk
index 6f32c4eb1..5ca8c14c1 100644
--- a/pkg/package.mk
+++ b/pkg/package.mk
@@ -2,10 +2,13 @@
 default: push
 
 ORG?=linuxkit
-HASH?=$(shell git ls-tree --full-tree HEAD -- $(CURDIR) | awk '{print $$3}')
+HASH_COMMIT?=HEAD # Setting this is only really useful with the show-tag target
+HASH?=$(shell git ls-tree --full-tree $(HASH_COMMIT) -- $(CURDIR) | awk '{print $$3}')
 BASE_DEPS=Dockerfile Makefile
 
+ifneq ($(HASH_COMMIT),HEAD) # Others can't be dirty by definition
 DIRTY=$(shell git diff-index --quiet HEAD -- $(CURDIR) || echo "-dirty")
+endif
 TAG=$(ORG)/$(IMAGE):$(HASH)$(DIRTY)
 
 # Get a release tag, if present