diff --git a/library/SMPP_CodecPort.ttcn b/library/SMPP_CodecPort.ttcn
index 0ac81ae..b415c09 100644
--- a/library/SMPP_CodecPort.ttcn
+++ b/library/SMPP_CodecPort.ttcn
@@ -9,6 +9,8 @@
  *
  * Released under the terms of GNU General Public License, Version 2 or
  * (at your option) any later version.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
  */