1 files changed, 4 insertions, 1 deletions
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index 64daff59df..abf53d149d 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -51,7 +51,10 @@ def _handle_frozendict(obj: Any) -> Dict[Any, Any]:
         # fishing the protected dict out of the object is a bit nasty,
         # but we don't really want the overhead of copying the dict.
         try:
-            return obj._dict
+            # Safety: we catch the AttributeError immediately below.
+            # See https://github.com/matrix-org/python-canonicaljson/issues/36#issuecomment-927816293
+            # for discussion on how frozendict's internals have changed over time.
+            return obj._dict  # type: ignore[attr-defined]
         except AttributeError:
             # When the C implementation of frozendict is used,
             # there isn't a `_dict` attribute with a dict