diff --git a/src/gsm/gsm0502.c b/src/gsm/gsm0502.c
index 6b69893..53259a4 100644
--- a/src/gsm/gsm0502.c
+++ b/src/gsm/gsm0502.c
@@ -4,6 +4,8 @@
  * (C) 2009 by Holger Hans Peter Freyther <zecke@selfish.org>
  * All Rights Reserved
  *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or