1 files changed, 3 insertions, 0 deletions
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 263d8ec076..cfe1bebb91 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -390,6 +390,9 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, RestServlet):
     async def on_POST(
         self, request: SynapseRequest, room_identifier: str
     ) -> Tuple[int, JsonDict]:
+        # This will always be set by the time Twisted calls us.
+        assert request.args is not None
+
         requester = await self.auth.get_user_by_req(request)
         await assert_user_is_admin(self.auth, requester.user)