diff --git a/log-tree.c b/log-tree.c
index f9385b1dae6f..9f50a81e537e 100644
--- a/log-tree.c
+++ b/log-tree.c

@@ -899,15 +899,21 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log
 	int showed_log;
 	struct commit_list *parents;
 	struct object_id *oid;
+	int is_merge;
+	int all_need_diff = opt->diff || opt->diffopt.flags.exit_with_status;
 
-	if (!opt->diff && !opt->diffopt.flags.exit_with_status)
+	if (!all_need_diff && !opt->merges_need_diff)
 		return 0;
 
 	parse_commit_or_die(commit);
 	oid = get_commit_tree_oid(commit);
 
-	/* Root commit? */
 	parents = get_saved_parents(opt, commit);
+	is_merge = parents && parents->next;
+	if (!is_merge && !all_need_diff)
+		return 0;
+
+	/* Root commit? */
 	if (!parents) {
 		if (opt->show_root_diff) {
 			diff_root_tree_oid(oid, "", &opt->diffopt);