diff --git a/lib/percpu_test.c b/lib/percpu_test.c
index 0b5d14d..4a3d70b 100644
--- a/lib/percpu_test.c
+++ b/lib/percpu_test.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/module.h>
 
 /* validate @native and @pcp counter values match @expected */