diff --git a/xen/include/public/io/sndif.h b/xen/include/public/io/sndif.h
index 667e610fda..916be1d3a1 100644
--- a/xen/include/public/io/sndif.h
+++ b/xen/include/public/io/sndif.h
@@ -680,6 +680,8 @@ struct xensnd_rw_req {
  * +----------------+----------------+----------------+----------------+
  * |                              length                               | 16
  * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
  * |                             reserved                              | 32
@@ -720,6 +722,8 @@ struct xensnd_rw_req {
  * +----------------+----------------+----------------+----------------+
  * |                              length                               | 16
  * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
  * |                             reserved                              | 32