1 files changed, 1 insertions, 1 deletions
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index c4ed9dfdb4..814145a04a 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -175,7 +175,7 @@ class PreviewUrlResource(DirectServeJsonResource):
             clock=self.clock,
             # don't spider URLs more often than once an hour
             expiry_ms=ONE_HOUR,
-        )
+        )  # type: ExpiringCache[str, ObservableDeferred]
 
         if self._worker_run_media_background_jobs:
             self._cleaner_loop = self.clock.looping_call(