diff --git a/synapse/rest/client/v2_alpha/shared_rooms.py b/synapse/rest/client/v2_alpha/shared_rooms.py
index 79998af1a3..944dd3dd2d 100644
--- a/synapse/rest/client/v2_alpha/shared_rooms.py
+++ b/synapse/rest/client/v2_alpha/shared_rooms.py
@@ -44,7 +44,7 @@ class UserSharedRoomsServlet(RestServlet):
 
         rooms = await self.store.get_rooms_in_common_for_users(user_id, other_user_id)
 
-        return 200, {"rooms": rooms,}
+        return 200, {"rooms": rooms}
 
 
 def register_servlets(hs, http_server):
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 0d668df0b6..24ac57f35d 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -60,6 +60,8 @@ class VersionsRestServlet(RestServlet):
                     "org.matrix.e2e_cross_signing": True,
                     # Implements additional endpoints as described in MSC2432
                     "org.matrix.msc2432": True,
+                    # Implements additional endpoints as described in MSC2666
+                    "uk.half-shot.msc2666": True,
                 },
             },
         )