diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 2b827b8..b5c1293 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * lib/locking-selftest.c
  *