diff --git a/passes/opt/opt_dff.cc b/passes/opt/opt_dff.cc
index cf68a0e89..f11326a05 100644
--- a/passes/opt/opt_dff.cc
+++ b/passes/opt/opt_dff.cc
@@ -2,6 +2,7 @@
  *  yosys -- Yosys Open SYnthesis Suite
  *
  *  Copyright (C) 2012  Claire Xenia Wolf <claire@yosyshq.com>
+ *  Copyright (C) 2020  Marcelina Kościelnicka <mwk@0x04.net>
  *
  *  Permission to use, copy, modify, and/or distribute this software for any
  *  purpose with or without fee is hereby granted, provided that the above