diff --git a/changelog.d/8385.bugfix b/changelog.d/8385.bugfix
new file mode 100644
index 0000000000..c42502a8e0
--- /dev/null
+++ b/changelog.d/8385.bugfix
@@ -0,0 +1 @@
+Fix a bug which could cause errors in rooms with malformed membership events, on servers using sqlite.
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index 7723d82496..18def01f50 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -17,7 +17,7 @@
 import itertools
 import logging
 from collections import OrderedDict, namedtuple
-from typing import TYPE_CHECKING, Dict, Iterable, List, Set, Tuple
+from typing import TYPE_CHECKING, Any, Dict, Iterable, List, Optional, Set, Tuple
 
 import attr
 from prometheus_client import Counter
@@ -1108,6 +1108,10 @@ class PersistEventsStore:
     def _store_room_members_txn(self, txn, events, backfilled):
         """Store a room member in the database.
         """
+
+        def str_or_none(val: Any) -> Optional[str]:
+            return val if isinstance(val, str) else None
+
         self.db_pool.simple_insert_many_txn(
             txn,
             table="room_memberships",
@@ -1118,8 +1122,8 @@ class PersistEventsStore:
                     "sender": event.user_id,
                     "room_id": event.room_id,
                     "membership": event.membership,
-                    "display_name": event.content.get("displayname", None),
-                    "avatar_url": event.content.get("avatar_url", None),
+                    "display_name": str_or_none(event.content.get("displayname")),
+                    "avatar_url": str_or_none(event.content.get("avatar_url")),
                 }
                 for event in events
             ],