diff --git a/protocol/proto/spirc.proto b/protocol/proto/spirc.proto
index 18fff490..9b4cdba9 100644
--- a/protocol/proto/spirc.proto
+++ b/protocol/proto/spirc.proto
@@ -67,6 +67,7 @@ enum CapabilityType {
     kVolumeSteps = 0x8;
     kSupportedTypes = 0x9;
     kCommandAcks = 0xa;
+    kUnknown = 0xb;
 }
 
 message Goodbye {