diff --git a/synapse/storage/filtering.py b/synapse/storage/filtering.py
index 700da8d8c..fcd43c7fd 100644
--- a/synapse/storage/filtering.py
+++ b/synapse/storage/filtering.py
@@ -34,7 +34,7 @@ class FilteringStore(SQLBaseStore):
             desc="get_user_filter",
         )
 
-        defer.returnValue(json.loads(def_json.decode("utf-8")))
+        defer.returnValue(json.loads(str(def_json).decode("utf-8")))
 
     def add_user_filter(self, user_localpart, user_filter):
         def_json = json.dumps(user_filter).encode("utf-8")