diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index 8a9b818..18e3cc3 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -714,7 +714,7 @@
 # @virtual: Win virtual bus type
 # @file-backed virtual: Win file-backed bus type
 #
-# Since: 2.2
+# Since: 2.2; 'Unknown' and all entries below since 2.4
 ##
 { 'enum': 'GuestDiskBusType',
   'data': [ 'ide', 'fdc', 'scsi', 'virtio', 'xen', 'usb', 'uml', 'sata',