1 files changed, 2 insertions, 2 deletions
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index 21b90b0674..22c85e497a 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -21,7 +21,7 @@
 import itertools
 import logging
 from collections import defaultdict
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
+from typing import TYPE_CHECKING, Any, Dict, List, Mapping, Optional, Tuple, Union
 
 from synapse.api.constants import AccountDataTypes, EduTypes, Membership, PresenceState
 from synapse.api.errors import Codes, StoreError, SynapseError
@@ -975,7 +975,7 @@ class SlidingSyncRestServlet(RestServlet):
         return response
 
     def encode_lists(
-        self, lists: Dict[str, SlidingSyncResult.SlidingWindowList]
+        self, lists: Mapping[str, SlidingSyncResult.SlidingWindowList]
     ) -> JsonDict:
         def encode_operation(
             operation: SlidingSyncResult.SlidingWindowList.Operation,