diff --git a/proto/protocol.xml b/proto/protocol.xml
index 7266aa4..c01c800 100644
--- a/proto/protocol.xml
+++ b/proto/protocol.xml
@@ -29,6 +29,9 @@
     SOFTWARE.
   </copyright>
 
+  <!-- The protocol documentation is available at
+       https://libinput.pages.freedesktop.org/libei/index.html -->
+
   <interface name="ei_handshake" version="1">
     <description summary="handshake object">
       This is a special interface to setup the client as seen by the EIS