diff --git a/merge.c b/merge.c
index 5db7d56b90..23866c9165 100644
--- a/merge.c
+++ b/merge.c
@@ -57,7 +57,8 @@ int checkout_fast_forward(const unsigned char *head,
 
 	refresh_cache(REFRESH_QUIET);
 
-	hold_locked_index(lock_file, 1);
+	if (hold_locked_index(lock_file, 0) < 0)
+		return -1;
 
 	memset(&trees, 0, sizeof(trees));
 	memset(&opts, 0, sizeof(opts));
@@ -90,7 +91,9 @@ int checkout_fast_forward(const unsigned char *head,
 	}
 	if (unpack_trees(nr_trees, t, &opts))
 		return -1;
-	if (write_locked_index(&the_index, lock_file, COMMIT_LOCK))
-		die(_("unable to write new index file"));
+	if (write_locked_index(&the_index, lock_file, COMMIT_LOCK)) {
+		rollback_lock_file(lock_file);
+		return error(_("unable to write new index file"));
+	}
 	return 0;
 }