diff --git a/bin/git-undo b/bin/git-undo
index 5cccbfe..bd561a8 100755
--- a/bin/git-undo
+++ b/bin/git-undo
@@ -64,7 +64,7 @@ EOL
     ;;
 esac
 
-if [[ ! $parm2 =~ [1-9]*([0-9]) ]]; then
+if [[ ! $parm2 =~ ^[1-9][0-9]*$ ]]; then
     echo "Invalid undo count: $parm2"
     exit 1
 fi