diff --git a/unstable/xdg-output/xdg-output-unstable-v1.xml b/unstable/xdg-output/xdg-output-unstable-v1.xml
index 9a5b790..f602da8 100644
--- a/unstable/xdg-output/xdg-output-unstable-v1.xml
+++ b/unstable/xdg-output/xdg-output-unstable-v1.xml
@@ -42,6 +42,10 @@
     concepts (such as output location within the global compositor space,
     the connector name and types, etc.) out of the core wl_output protocol.
 
+    Compositors implementing version 3 of this protocol must support
+    wl_output v2 or higher. Clients binding to this protocol at version 3 must
+    also bind to wl_output objects at version 2 or higher.
+
     Warning! The protocol described in this file is experimental and
     backward incompatible changes may be made. Backward compatible
     changes may be added together with the corresponding interface