diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index 06f9eee9f7..914ec960b7 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -366,15 +366,12 @@ static void *get_tree_descriptor(struct repository *r,
 	return buf;
 }
 
-int cmd_merge_tree(int argc, const char **argv, const char *prefix)
+static int trivial_merge(int argc, const char **argv)
 {
 	struct repository *r = the_repository;
 	struct tree_desc t[3];
 	void *buf1, *buf2, *buf3;
 
-	if (argc != 4)
-		usage(merge_tree_usage);
-
 	buf1 = get_tree_descriptor(r, t+0, argv[1]);
 	buf2 = get_tree_descriptor(r, t+1, argv[2]);
 	buf3 = get_tree_descriptor(r, t+2, argv[3]);
@@ -386,3 +383,10 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 	show_result();
 	return 0;
 }
+
+int cmd_merge_tree(int argc, const char **argv, const char *prefix)
+{
+	if (argc != 4)
+		usage(merge_tree_usage);
+	return trivial_merge(argc, argv);
+}