diff --git a/git-commit.sh b/git-commit.sh
index 7a7a2cb4b4..ab43217be4 100755
--- a/git-commit.sh
+++ b/git-commit.sh
@@ -25,6 +25,7 @@ refuse_partial () {
 	exit 1
 }
 
+TMP_INDEX=
 THIS_INDEX="$GIT_DIR/index"
 NEXT_INDEX="$GIT_DIR/next-index$$"
 rm -f "$NEXT_INDEX"