diff --git a/mkreleasehdr.sh b/mkreleasehdr.sh
index ea3b35a58..c458e6480 100755
--- a/mkreleasehdr.sh
+++ b/mkreleasehdr.sh
@@ -1,5 +1,5 @@
 #!/bin/sh
-GIT_SHA1=$(git show-ref --head --hash=8 2> /dev/null | head -n1)
+GIT_SHA1=$( (git show-ref --head --hash=8 2> /dev/null || echo 00000000) | head -n1)
 GIT_DIRTY=$(git diff 2> /dev/null | wc -l)
 test -f release.h || touch release.h
 (cat release.h | grep SHA1 | grep $GIT_SHA1) && \