diff --git a/spice/protocol.h b/spice/protocol.h
index 26d964b..40027be 100644
--- a/spice/protocol.h
+++ b/spice/protocol.h
@@ -103,10 +103,12 @@ typedef struct SPICE_ATTR_PACKED SpiceSubMessageList {
 
 enum {
     SPICE_PLAYBACK_CAP_CELT_0_5_1,
+    SPICE_PLAYBACK_CAP_VOLUME,
 };
 
 enum {
     SPICE_RECORD_CAP_CELT_0_5_1,
+    SPICE_RECORD_CAP_VOLUME,
 };
 
 #include <spice/end-packed.h>