diff --git a/include/linux/pid.h b/include/linux/pid.h
index 7195827..dfd684c 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _LINUX_PID_H
 #define _LINUX_PID_H