diff --git a/data/api/server-server/joins-v2.yaml b/data/api/server-server/joins-v2.yaml
index 49467c21..1248c0c9 100644
--- a/data/api/server-server/joins-v2.yaml
+++ b/data/api/server-server/joins-v2.yaml
@@ -255,6 +255,7 @@ paths:
                   server's signature.
               servers_in_room:
                 type: array
+                x-addedInMatrixVersion: "1.6"
                 description: |-
                   **Required** if `members_omitted` is true.