diff --git a/helper/git-extra-utility b/helper/git-extra-utility
index 98ed09f..ff3c41f 100755
--- a/helper/git-extra-utility
+++ b/helper/git-extra-utility
@@ -2,6 +2,6 @@
 
 # make a temporary file
 git_extra_mktemp() {
-    mktemp -t "$(basename "$0")".XXX
+    mktemp -t "$(basename "$0")".XXXXXXX
 }