diff --git a/spec/integ/matrix-client-event-timeline.spec.js b/spec/integ/matrix-client-event-timeline.spec.js
index ad475f3fc5a..6e93a063a8d 100644
--- a/spec/integ/matrix-client-event-timeline.spec.js
+++ b/spec/integ/matrix-client-event-timeline.spec.js
@@ -496,6 +496,7 @@ describe("MatrixClient event timelines", function() {
         });
 
         it("should handle thread replies with server support by fetching a contiguous thread timeline", async () => {
+            client.clientOpts.experimentalThreadSupport = true;
             Thread.setServerSideSupport(true);
             client.stopClient(); // we don't need the client to be syncing at this time
             const room = client.getRoom(roomId);
diff --git a/src/client.ts b/src/client.ts
index bc55145e557..a601c96de24 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -3776,7 +3776,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         const thread = room?.threads.get(threadId);
         if (thread) {
             localEvent.setThread(thread);
-            localEvent.setThreadId(thread.id);
         }
 
         // set up re-emitter for this new event - this is normally the job of EventMapper but we don't use it here
@@ -5278,7 +5277,10 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         // Where the event is a thread reply (not a root) and running in MSC-enabled mode the Thread timeline only
         // functions contiguously, so we have to jump through some hoops to get our target event in it.
         // XXX: workaround for https://github.com/vector-im/element-meta/issues/150
-        if (Thread.hasServerSideSupport && event.isRelation(THREAD_RELATION_TYPE.name)) {
+        if (Thread.hasServerSideSupport &&
+            this.supportsExperimentalThreads() &&
+            event.isRelation(THREAD_RELATION_TYPE.name)
+        ) {
             const [, threadedEvents] = timelineSet.room.partitionThreadedEvents(events);
             const thread = await timelineSet.room.createThreadFetchRoot(event.threadRootId, threadedEvents, true);
 
diff --git a/src/models/room.ts b/src/models/room.ts
index af3dd4758b8..a02b4f9511a 100644
--- a/src/models/room.ts
+++ b/src/models/room.ts
@@ -1474,7 +1474,7 @@ export class Room extends TypedEventEmitter<EmittedEvents, RoomEventHandlerMap>
     public threadsReady = false;
 
     public async fetchRoomThreads(): Promise<void> {
-        if (this.threadsReady) {
+        if (this.threadsReady || !this.client.supportsExperimentalThreads()) {
             return;
         }
 
@@ -1662,7 +1662,7 @@ export class Room extends TypedEventEmitter<EmittedEvents, RoomEventHandlerMap>
                 // benefit from all the APIs a homeserver can provide to enhance the thread experience
                 thread = this.createThread(rootEvent, events, toStartOfTimeline);
                 if (thread) {
-                    rootEvent.setThread(thread);
+                    rootEvent?.setThread(thread);
                 }
                 deferred.resolve(thread);
             }