1 files changed, 1 insertions, 1 deletions
diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index c981df3f18..5cf2e12575 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -118,7 +118,7 @@ class _StateCacheEntry:
         else:
             self.state_id = _gen_state_id()
 
-    def __len__(self):
+    def __len__(self) -> int:
         return len(self.state)