diff --git a/lib/test_module.c b/lib/test_module.c
index 319b66f..debd19e 100644
--- a/lib/test_module.c
+++ b/lib/test_module.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * This module emits "Hello, world" on printk when loaded.
  *