--- a/make-rules/prep-git.mk	Mon Nov 16 21:09:02 2015 -0800
+++ b/make-rules/prep-git.mk	Tue Nov 17 07:45:07 2015 -0800
@@ -34,8 +34,8 @@
 ifdef GIT_REPO$(1)
 ifdef GIT_COMMIT_ID$(1)
 
-COMPONENT_SRC$(1) = $$(COMPONENT_NAME$(1))-$$(GIT_COMMIT_ID$(1))
-COMPONENT_ARCHIVE$(1) = $$(COMPONENT_SRC$(1)).tar.gz
+COMPONENT_SRC$(1) ?= $$(COMPONENT_NAME$(1))-$$(GIT_COMMIT_ID$(1))
+COMPONENT_ARCHIVE$(1) ?= $$(COMPONENT_SRC$(1)).tar.gz
 
 CLEAN_PATHS += $$(COMPONENT_SRC$(1))
 CLOBBER_PATHS += $$(COMPONENT_ARCHIVE$(1))