diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 545d99b..ba27f7a 100644
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef __USBMIXER_H
 #define __USBMIXER_H