diff --git a/data/event-schemas/schema/m.call.invite.yaml b/data/event-schemas/schema/m.call.invite.yaml
index 194420d7..3693e225 100644
--- a/data/event-schemas/schema/m.call.invite.yaml
+++ b/data/event-schemas/schema/m.call.invite.yaml
@@ -34,6 +34,8 @@ properties:
         type: string
         description: The ID of the user being called. If omitted, any user in the room can answer.
         x-addedInMatrixVersion: '1.7'
+        format: mx-user-id
+        pattern: "^@"
       sdp_stream_metadata:
         $ref: components/sdp_stream_metadata.yaml
     required: