diff --git a/crates/matrix-sdk-ui/src/room_list_service/mod.rs b/crates/matrix-sdk-ui/src/room_list_service/mod.rs
index 6fc9d3a634c..3331b58082c 100644
--- a/crates/matrix-sdk-ui/src/room_list_service/mod.rs
+++ b/crates/matrix-sdk-ui/src/room_list_service/mod.rs
@@ -67,12 +67,14 @@ use matrix_sdk::{
 };
 pub use room_list::*;
 use ruma::{
-    OwnedRoomId, RoomId, UInt, api::client::sync::sync_events::v5 as http, assign,
+    OwnedRoomId, RoomId, UInt,
+    api::{FeatureFlag, client::sync::sync_events::v5 as http},
+    assign,
     events::StateEventType,
 };
 pub use state::*;
 use thiserror::Error;
-use tracing::{debug, error};
+use tracing::{debug, error, warn};
 
 /// The default `required_state` constant value for sliding sync lists and
 /// sliding sync room subscriptions.
@@ -156,12 +158,25 @@ impl RoomListService {
             }));
 
         if client.enabled_thread_subscriptions() {
-            builder = builder.with_thread_subscriptions_extension(
-                assign!(http::request::ThreadSubscriptions::default(), {
-                    enabled: Some(true),
-                    limit: Some(ruma::uint!(10))
-                }),
-            );
+            let server_features = client
+                .supported_versions()
+                .await
+                .map_err(|err| Error::SlidingSync(err.into()))?
+                .features;
+
+            if !server_features.contains(&FeatureFlag::from("org.matrix.msc4306")) {
+                warn!(
+                    "Thread subscriptions extension is requested on the client, but the server doesn't advertise support for it: not enabling."
+                );
+            } else {
+                debug!("Enabling the thread subscriptions extension");
+                builder = builder.with_thread_subscriptions_extension(
+                    assign!(http::request::ThreadSubscriptions::default(), {
+                        enabled: Some(true),
+                        limit: Some(ruma::uint!(10))
+                    }),
+                );
+            }
         }
 
         if share_pos {
diff --git a/crates/matrix-sdk-ui/tests/integration/room_list_service.rs b/crates/matrix-sdk-ui/tests/integration/room_list_service.rs
index 0ceb2d8d373..48f0d1198c7 100644
--- a/crates/matrix-sdk-ui/tests/integration/room_list_service.rs
+++ b/crates/matrix-sdk-ui/tests/integration/room_list_service.rs
@@ -1,4 +1,4 @@
-use std::{ops::Not, sync::Arc};
+use std::{collections::BTreeMap, ops::Not, sync::Arc};
 
 use assert_matches::assert_matches;
 use eyeball_im::VectorDiff;
@@ -2893,3 +2893,196 @@ async fn test_multiple_timeline_init() {
     // A new timeline for the same room can still be constructed.
     room.timeline_builder().build().await.unwrap();
 }
+
+#[async_test]
+async fn test_thread_subscriptions_extension_enabled_only_if_server_advertises_it() {
+    let server = MatrixMockServer::new().await;
+
+    {
+        // The first time, don't advertise support for MSC4306; the extension will NOT
+        // enabled in this case, despite the client requesting it.
+        let features_map = BTreeMap::new();
+
+        server
+            .mock_versions()
+            .ok_custom(&["v1.11"], &features_map)
+            .named("/versions, first time")
+            .mock_once()
+            .mount()
+            .await;
+
+        let client = server
+            .client_builder()
+            .no_server_versions()
+            .on_builder(|b| {
+                b.with_threading_support(matrix_sdk::ThreadingSupport::Enabled {
+                    with_subscriptions: true,
+                })
+            })
+            .build()
+            .await;
+        let room_list = RoomListService::new(client.clone()).await.unwrap();
+
+        let sync = room_list.sync();
+        pin_mut!(sync);
+
+        let room_id = room_id!("!r0:bar.org");
+
+        let mock_server = server.server();
+        sync_then_assert_request_and_fake_response! {
+            [mock_server, room_list, sync]
+            assert request = {
+                "conn_id": "room-list",
+                "extensions": {
+                    "account_data": {
+                        "enabled": true,
+                    },
+                    "receipts": {
+                        "enabled": true,
+                        "rooms": ["*"],
+                    },
+                    "typing": {
+                        "enabled": true,
+                    },
+                },
+                "lists": {
+                    "all_rooms": {
+                        "filters": {},
+                        "ranges": [ [ 0, 19, ], ],
+                        "required_state": [
+                            [ "m.room.name", "" ],
+                            [ "m.room.encryption", "" ],
+                            [ "m.room.member", "$LAZY" ],
+                            [ "m.room.member", "$ME" ],
+                            [ "m.room.topic", "", ],
+                            [ "m.room.avatar", "", ],
+                            [ "m.room.canonical_alias", "", ],
+                            [ "m.room.power_levels", "", ],
+                            [ "org.matrix.msc3401.call.member", "*", ],
+                            [ "m.room.join_rules", "", ],
+                            [ "m.room.tombstone", "", ],
+                            [ "m.room.create", "", ],
+                            [ "m.room.history_visibility", "", ],
+                            [ "io.element.functional_members", "", ],
+                            [ "m.space.parent", "*", ],
+                            [ "m.space.child", "*", ],
+                        ],
+                        "timeline_limit": 1,
+                    },
+                },
+            },
+            respond with = {
+                "pos": "0",
+                "lists": {
+                    ALL_ROOMS: {
+                        "count": 2,
+                    },
+                },
+                "rooms": {
+                    room_id: {
+                        "initial": true,
+                        "timeline": [
+                            timeline_event!("$x0:bar.org" at 0 sec),
+                        ],
+                        "prev_batch": "prev-batch-token"
+                    },
+                },
+            },
+        };
+    }
+
+    // Then, advertise support with support for MSC4306; the extension will be
+    // enabled in this case.
+    let features_map = BTreeMap::from([("org.matrix.msc4306", true)]);
+
+    server
+        .mock_versions()
+        .ok_custom(&["v1.11"], &features_map)
+        .named("/versions, second time")
+        .mock_once()
+        .mount()
+        .await;
+
+    let client = server
+        .client_builder()
+        .no_server_versions()
+        .on_builder(|b| {
+            b.with_threading_support(matrix_sdk::ThreadingSupport::Enabled {
+                with_subscriptions: true,
+            })
+        })
+        .build()
+        .await;
+    let room_list = RoomListService::new(client.clone()).await.unwrap();
+
+    let sync = room_list.sync();
+    pin_mut!(sync);
+
+    let room_id = room_id!("!r0:bar.org");
+
+    let mock_server = server.server();
+    sync_then_assert_request_and_fake_response! {
+        [mock_server, room_list, sync]
+        assert request = {
+            "conn_id": "room-list",
+            "extensions": {
+                "account_data": {
+                    "enabled": true,
+                },
+                "receipts": {
+                    "enabled": true,
+                    "rooms": ["*"],
+                },
+                "typing": {
+                    "enabled": true,
+                },
+                "io.element.msc4308.thread_subscriptions": {
+                    "enabled": true,
+                    "limit": 10,
+                },
+            },
+            "lists": {
+                "all_rooms": {
+                    "filters": {},
+                    "ranges": [ [ 0, 19, ], ],
+                    "required_state": [
+                        [ "m.room.name", "" ],
+                        [ "m.room.encryption", "" ],
+                        [ "m.room.member", "$LAZY" ],
+                        [ "m.room.member", "$ME" ],
+                        [ "m.room.topic", "", ],
+                        [ "m.room.avatar", "", ],
+                        [ "m.room.canonical_alias", "", ],
+                        [ "m.room.power_levels", "", ],
+                        [ "org.matrix.msc3401.call.member", "*", ],
+                        [ "m.room.join_rules", "", ],
+                        [ "m.room.tombstone", "", ],
+                        [ "m.room.create", "", ],
+                        [ "m.room.history_visibility", "", ],
+                        [ "io.element.functional_members", "", ],
+                        [ "m.space.parent", "*", ],
+                        [ "m.space.child", "*", ],
+                    ],
+                    "timeline_limit": 1,
+                },
+            },
+        },
+        respond with = {
+            "pos": "0",
+            "lists": {
+                ALL_ROOMS: {
+                    "count": 2,
+                },
+            },
+            "rooms": {
+                room_id: {
+                    "initial": true,
+                    "timeline": [
+                        timeline_event!("$x0:bar.org" at 0 sec),
+                    ],
+                    "prev_batch": "prev-batch-token"
+                },
+            },
+        },
+    };
+}
diff --git a/crates/matrix-sdk/src/test_utils/client.rs b/crates/matrix-sdk/src/test_utils/client.rs
index c86eadc5bba..2c5ade29b47 100644
--- a/crates/matrix-sdk/src/test_utils/client.rs
+++ b/crates/matrix-sdk/src/test_utils/client.rs
@@ -54,7 +54,7 @@ impl MockClientBuilder {
         }
     }
 
-    /// Don't cache server versions in the client.
+    /// Don't use an initial, cached server versions list in the client.
     pub fn no_server_versions(mut self) -> Self {
         self.server_versions = ServerVersions::None;
         self