diff --git a/combine-diff.c b/combine-diff.c
index b724f02123..b0ece95480 100644
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -1498,6 +1498,13 @@ void diff_tree_combined(const struct object_id *oid,
 	int i, num_paths, needsep, show_log_first, num_parent = parents->nr;
 	int need_generic_pathscan;
 
+	if (opt->ignore_regex_nr)
+		die("combined diff and '%s' cannot be used together",
+		    "--ignore-matching-lines");
+	if (opt->close_file)
+		die("combined diff and '%s' cannot be used together",
+		    "--output");
+
 	/* nothing to do, if no parents */
 	if (!num_parent)
 		return;