diff --git a/builtin-diff-tree.c b/builtin-diff-tree.c
index ae1cde9d00..1e66fcac21 100644
--- a/builtin-diff-tree.c
+++ b/builtin-diff-tree.c
@@ -72,6 +72,7 @@ int cmd_diff_tree(int argc, const char **argv, char **envp)
 	init_revisions(opt);
 	opt->abbrev = 0;
 	opt->diff = 1;
+	opt->diffopt.msg_sep = "---\n";
 	argc = setup_revisions(argc, argv, opt, NULL);
 
 	while (--argc > 0) {