diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index ea1ad036b2..5e658b0764 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -429,6 +429,17 @@ class ClientEvent:
     event: "EventBase"
     membership: str | None
 
+    @classmethod
+    def state(cls, event: "EventBase") -> "ClientEvent":
+        """Wrap a state event with no per-user membership annotation.
+
+        The event must be a state event (i.e. have a state_key).
+        """
+        assert event.is_state(), (
+            f"ClientEvent.state() called with non-state event {event.event_id}"
+        )
+        return cls(event=event, membership=None)
+
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)
 class SerializeEventConfig:
diff --git a/synapse/handlers/initial_sync.py b/synapse/handlers/initial_sync.py
index 9b1eeced16..df78457838 100644
--- a/synapse/handlers/initial_sync.py
+++ b/synapse/handlers/initial_sync.py
@@ -252,10 +252,7 @@ class InitialSyncHandler:
                 }
 
                 d["state"] = await self._event_serializer.serialize_events(
-                    [
-                        ClientEvent(event=e, membership=None)
-                        for e in current_state.values()
-                    ],
+                    [ClientEvent.state(e) for e in current_state.values()],
                     time_now=time_now,
                     config=serializer_options,
                 )
@@ -418,10 +415,7 @@ class InitialSyncHandler:
             "state": (
                 # Don't bundle aggregations as this is a deprecated API.
                 await self._event_serializer.serialize_events(
-                    [
-                        ClientEvent(event=e, membership=None)
-                        for e in room_state.values()
-                    ],
+                    [ClientEvent.state(e) for e in room_state.values()],
                     time_now,
                     config=serialize_options,
                 )
@@ -447,7 +441,7 @@ class InitialSyncHandler:
         serialize_options = SerializeEventConfig(requester=requester)
         # Don't bundle aggregations as this is a deprecated API.
         state = await self._event_serializer.serialize_events(
-            [ClientEvent(event=e, membership=None) for e in current_state.values()],
+            [ClientEvent.state(e) for e in current_state.values()],
             time_now,
             config=serialize_options,
         )
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 164aff6bf0..ceb1523eca 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -265,7 +265,7 @@ class MessageHandler:
                 room_state = room_state_events[membership_event_id]
 
         events = await self._event_serializer.serialize_events(
-            [ClientEvent(event=e, membership=None) for e in room_state.values()],
+            [ClientEvent.state(e) for e in room_state.values()],
             self.clock.time_msec(),
             config=SerializeEventConfig(requester=requester),
         )
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index c47736889e..6c6816efbc 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -416,7 +416,7 @@ class SearchHandler:
         if state_results:
             rooms_cat_res["state"] = {
                 room_id: await self._event_serializer.serialize_events(
-                    [ClientEvent(event=e, membership=None) for e in state_events],
+                    [ClientEvent.state(e) for e in state_events],
                     time_now,
                     config=serialize_options,
                 )
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 6596affefb..4d9cda807a 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -531,7 +531,7 @@ class RoomStateRestServlet(RestServlet):
         events = await self.store.get_events(event_ids.values())
         now = self.clock.time_msec()
         room_state = await self._event_serializer.serialize_events(
-            [ClientEvent(event=e, membership=None) for e in events.values()], now
+            [ClientEvent.state(e) for e in events.values()], now
         )
         ret = {"state": room_state}
 
@@ -900,7 +900,7 @@ class RoomEventContextServlet(RestServlet):
                 bundle_aggregations=event_context.aggregations,
             ),
             "state": await self._event_serializer.serialize_events(
-                [ClientEvent(event=e, membership=None) for e in event_context.state],
+                [ClientEvent.state(e) for e in event_context.state],
                 time_now,
             ),
             "start": event_context.start,
diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index 1122e39969..87126db8a4 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -287,7 +287,7 @@ class RoomStateEventRestServlet(RestServlet):
 
         if format == "event":
             event = await self._event_serializer.serialize_event(
-                ClientEvent(event=data, membership=None),
+                ClientEvent.state(data),
                 self.clock.time_msec(),
                 config=SerializeEventConfig(
                     event_format=format_event_for_client_v2,
@@ -867,7 +867,7 @@ async def encode_messages_response(
         serialized_result[
             "state"
         ] = await serialize_deps.event_serializer.serialize_events(
-            [ClientEvent(event=e, membership=None) for e in get_messages_result.state],
+            [ClientEvent.state(e) for e in get_messages_result.state],
             time_now,
             config=serialize_options,
         )
@@ -1175,7 +1175,7 @@ class RoomEventContextServlet(RestServlet):
                 config=serializer_options,
             ),
             "state": await self._event_serializer.serialize_events(
-                [ClientEvent(event=e, membership=None) for e in event_context.state],
+                [ClientEvent.state(e) for e in event_context.state],
                 time_now,
                 config=serializer_options,
             ),
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index 9ad06d9fd3..97f84eb764 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -600,7 +600,7 @@ class SyncRestServlet(RestServlet):
                 )
 
         serialized_state = await self._event_serializer.serialize_events(
-            [ClientEvent(event=e, membership=None) for e in state_events],
+            [ClientEvent.state(e) for e in state_events],
             time_now,
             config=serialize_options,
         )
@@ -990,10 +990,7 @@ class SlidingSyncRestServlet(RestServlet):
             ):
                 serialized_required_state = (
                     await self.event_serializer.serialize_events(
-                        [
-                            ClientEvent(event=e, membership=None)
-                            for e in room_result.required_state
-                        ],
+                        [ClientEvent.state(e) for e in room_result.required_state],
                         time_now,
                         config=serialize_options,
                     )