diff --git a/src/gsm/gsm0808.c b/src/gsm/gsm0808.c
index ee5eda4..2396a10 100644
--- a/src/gsm/gsm0808.c
+++ b/src/gsm/gsm0808.c
@@ -3,6 +3,8 @@
  * (C) 2009,2010 by On-Waves
  * 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