diff --git a/Documentation/sound/index.rst b/Documentation/sound/index.rst
index 5abed5fc6485..7e67e12730d3 100644
--- a/Documentation/sound/index.rst
+++ b/Documentation/sound/index.rst
@@ -1,3 +1,5 @@
+.. SPDX-License-Identifier: GPL-2.0
+
 =============================
 Sound Subsystem Documentation
 =============================