diff --git a/data/api/server-server/joins-v2.yaml b/data/api/server-server/joins-v2.yaml
index 55f68ea9..465207e9 100644
--- a/data/api/server-server/joins-v2.yaml
+++ b/data/api/server-server/joins-v2.yaml
@@ -207,8 +207,9 @@ paths:
                     title: SignedMembershipEvent
                     x-addedInMatrixVersion: "1.2"
                     description: |-
-                      The signed copy of the membership event sent to other servers by the resident server.
-                      Required if the event is signed by the resident server.
+                      The membership event sent to other servers by the resident server including a signature
+                      from the resident server. Required if the room is [restricted](/client-server-api/#restricted-rooms)
+                      and the joining user is authorised by one of the conditions.
                   servers_in_room:
                     type: array
                     x-addedInMatrixVersion: "1.6"