diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py

index 8d845fe951..3b3a089b76 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -670,6 +670,16 @@ class DeviceWorkerStore(SQLBaseStore):
             device["device_id"]: db_to_json(device["content"]) for device in devices
         }
 
+    def get_cached_device_list_changes(
+        self,
+        from_key: int,
+    ) -> Optional[Set[str]]:
+        """Get set of users whose devices have changed since `from_key`, or None
+        if that information is not in our cache.
+        """
+
+        return self._device_list_stream_cache.get_all_entities_changed(from_key)
+
     async def get_users_whose_devices_changed(
         self, from_key: int, user_ids: Iterable[str]
     ) -> Set[str]: