diff --git a/Makefile.include b/Makefile.include
index 09f69e43f..11bf809b9 100644
--- a/Makefile.include
+++ b/Makefile.include
@@ -153,7 +153,7 @@ CFLAGS += ${addprefix -I,$(SOURCEDIRS) $(CONTIKI)}
 ### Check for a git repo and pass version if found
 ### git.exe in Windows cmd shells may require no stderr redirection
 #RELSTR=${shell git describe --tags}
-RELSTR=${shell git --git-dir ${CONTIKI}/.git describe --tags 2>/dev/null}
+RELSTR:=${shell git --git-dir ${CONTIKI}/.git describe --tags 2>/dev/null}
 ifneq ($(RELSTR),)
 CFLAGS += -DCONTIKI_VERSION_STRING=\"Contiki-$(RELSTR)\"
 endif