1 files changed, 18 insertions, 4 deletions
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 8b247fe206..d963178838 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -15,7 +15,19 @@
 
 import logging
 import urllib
-from typing import Any, Callable, Dict, Iterable, List, Mapping, Optional, Tuple, Union
+from typing import (
+    Any,
+    Awaitable,
+    Callable,
+    Collection,
+    Dict,
+    Iterable,
+    List,
+    Mapping,
+    Optional,
+    Tuple,
+    Union,
+)
 
 import attr
 import ijson
@@ -100,7 +112,7 @@ class TransportLayerClient:
 
     @log_function
     async def backfill(
-        self, destination: str, room_id: str, event_tuples: Iterable[str], limit: int
+        self, destination: str, room_id: str, event_tuples: Collection[str], limit: int
     ) -> Optional[JsonDict]:
         """Requests `limit` previous PDUs in a given context before list of
         PDUs.
@@ -108,7 +120,9 @@ class TransportLayerClient:
         Args:
             destination
             room_id
-            event_tuples
+            event_tuples:
+                Must be a Collection that is falsy when empty.
+                (Iterable is not enough here!)
             limit
 
         Returns:
@@ -786,7 +800,7 @@ class TransportLayerClient:
     @log_function
     def join_group(
         self, destination: str, group_id: str, user_id: str, content: JsonDict
-    ) -> JsonDict:
+    ) -> Awaitable[JsonDict]:
         """Attempts to join a group"""
         path = _create_v1_path("/groups/%s/users/%s/join", group_id, user_id)