diff --git a/make-tarball.sh b/make-tarball.sh
index b0c0b8b..7020310 100755
--- a/make-tarball.sh
+++ b/make-tarball.sh
@@ -3,15 +3,16 @@
 # args
 repo="${1%/}"
 ref="${2-HEAD}"
+ab="${3-12}"
 
 # check
 if test ! -d "${repo}/.git"; then
-    echo "usage: $0 <repodir> [ <ref> ]"
+    echo "usage: $0 <repodir> [ <ref> [ <abbrev> ] ]"
     exit 1
 fi
 
 # get + print info
-commit=$(cd $repo; git show --pretty='format:%h' $ref | head -1)
+commit=$(cd $repo; git show --abbrev=$ab --pretty='format:%h' $ref | head -1)
 date=$(cd $repo; git show --pretty='format:%cs' $ref | head -1 | tr -d '-')
 echo "# $repo $ref  ->  commit $commit - date $date"