diff --git a/git-filter-branch.sh b/git-filter-branch.sh
old mode 100755
new mode 100644
index c22266b486..6cf67df5d6
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -13,6 +13,10 @@ set -e
 USAGE="git-filter-branch [-d TEMPDIR] [FILTERS] DESTBRANCH [REV-RANGE]"
 . git-sh-setup
 
+warn () {
+        echo "$*" >&2
+}
+
 map()
 {
 	# if it was not rewritten, take the original