diff --git a/tools/git-applymbox b/tools/git-applymbox
index 889d4c1743ccdfcf8ad0be96a58eb8b60c03ccdc..afcb00a3f5e25d062eb1219994506a669e252bc5 100755
--- a/tools/git-applymbox
+++ b/tools/git-applymbox
@@ -18,6 +18,8 @@
 ## use a Signoff_file, because applypatch wants to append the sign-off
 ## message to msg-clean every time it is run.
 
+. git-sh-setup-script || die "Not a git archive"
+
 keep_subject= query_apply= continue= resume=t
 while case "$#" in 0) break ;; esac
 do
@@ -39,6 +41,12 @@ case "$continue" in
 	shift
 esac
 
+files=$(git-diff-cache --cached --name-only HEAD) || exit
+if [ "$files" ]; then
+   echo "Dirty index: cannot apply patches (dirty: $files)" >&2
+   exit 1
+fi
+
 case "$query_apply" in
 t)	touch .dotest/.query_apply
 esac