diff --git a/Makefile b/Makefile
index 1785904a..ff0af4c1 100644
--- a/Makefile
+++ b/Makefile
@@ -72,8 +72,9 @@ else
 	LDLIBS += -lrt
 endif
 
+GIT_REV_WHERE ?= HEAD
 YOSYS_VER := 0.6+$(shell test -e .git && { git log --author=clifford@clifford.at --oneline 5869d26da021.. | wc -l; })
-GIT_REV := $(shell cd $(YOSYS_SRC) && git rev-parse --short HEAD 2> /dev/null || echo UNKNOWN)
+GIT_REV := $(shell cd $(YOSYS_SRC) && git rev-parse --short $(GIT_REV_WHERE) 2> /dev/null || echo UNKNOWN)
 OBJS = kernel/version_$(GIT_REV).o
 
 # set 'ABCREV = default' to use abc/ as it is