diff --git a/crates/matrix-sdk-ui/tests/integration/timeline/mod.rs b/crates/matrix-sdk-ui/tests/integration/timeline/mod.rs
index cdb3cfda3..bd65ec865 100644
--- a/crates/matrix-sdk-ui/tests/integration/timeline/mod.rs
+++ b/crates/matrix-sdk-ui/tests/integration/timeline/mod.rs
@@ -48,6 +48,7 @@ mod pagination;
 mod pinned_event;
 mod profiles;
 mod queue;
+mod reactions;
 mod read_receipts;
 mod replies;
 mod subscribe;
diff --git a/crates/matrix-sdk-ui/tests/integration/timeline/reactions.rs b/crates/matrix-sdk-ui/tests/integration/timeline/reactions.rs
new file mode 100644
index 000000000..fc7e2bb90
--- /dev/null
+++ b/crates/matrix-sdk-ui/tests/integration/timeline/reactions.rs
@@ -0,0 +1,173 @@
+// Copyright 2024 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::time::Duration;
+
+use assert_matches2::{assert_let, assert_matches};
+use eyeball_im::VectorDiff;
+use futures_util::{FutureExt as _, StreamExt as _};
+use matrix_sdk::test_utils::{events::EventFactory, logged_in_client_with_server};
+use matrix_sdk_test::{
+    async_test,
+    mocks::{mock_encryption_state, mock_redaction},
+    JoinedRoomBuilder, SyncResponseBuilder, ALICE,
+};
+use matrix_sdk_ui::timeline::{ReactionStatus, RoomExt as _};
+use ruma::{event_id, events::relation::Annotation, room_id};
+use serde_json::json;
+use wiremock::{
+    matchers::{header, method, path_regex},
+    Mock, ResponseTemplate,
+};
+
+use crate::mock_sync;
+
+#[async_test]
+async fn test_abort_before_being_sent() {
+    // This test checks that a reaction could be aborted *before* or *while* it's
+    // being sent by the send queue.
+
+    let room_id = room_id!("!a98sd12bjh:example.org");
+    let (client, server) = logged_in_client_with_server().await;
+    let user_id = client.user_id().unwrap();
+
+    // Make the test aware of the room.
+    let mut sync_builder = SyncResponseBuilder::new();
+    sync_builder.add_joined_room(JoinedRoomBuilder::new(room_id));
+
+    mock_sync(&server, sync_builder.build_json_sync_response(), None).await;
+    let _response = client.sync_once(Default::default()).await.unwrap();
+    server.reset().await;
+
+    mock_encryption_state(&server, false).await;
+
+    let room = client.get_room(room_id).unwrap();
+    let timeline = room.timeline().await.unwrap();
+    let (initial_items, mut stream) = timeline.subscribe().await;
+
+    assert!(initial_items.is_empty());
+
+    let f = EventFactory::new();
+
+    let event_id = event_id!("$1");
+    sync_builder.add_joined_room(
+        JoinedRoomBuilder::new(room_id)
+            .add_timeline_event(f.text_msg("hello").sender(&ALICE).event_id(event_id)),
+    );
+
+    mock_sync(&server, sync_builder.build_json_sync_response(), None).await;
+    let _response = client.sync_once(Default::default()).await.unwrap();
+    server.reset().await;
+
+    assert_let!(Some(VectorDiff::PushBack { value: first }) = stream.next().await);
+    let item = first.as_event().unwrap();
+    assert_eq!(item.content().as_message().unwrap().body(), "hello");
+
+    assert_let!(Some(VectorDiff::PushFront { value: day_divider }) = stream.next().await);
+    assert!(day_divider.is_day_divider());
+
+    // Now we try to add two reactions to this message…
+
+    // Mock the send endpoint with a delay, to give us time to abort the sending.
+    Mock::given(method("PUT"))
+        .and(path_regex(r"^/_matrix/client/r0/rooms/.*/send/.*"))
+        .and(header("authorization", "Bearer 1234"))
+        .respond_with(
+            ResponseTemplate::new(200)
+                .set_body_json(json!({
+                    "event_id": "$2",
+                }))
+                .set_delay(Duration::from_millis(150)),
+        )
+        .expect(1)
+        .named("send")
+        .mount(&server)
+        .await;
+
+    mock_redaction(event_id!("$3")).mount(&server).await;
+
+    // We add the reaction…
+    timeline.toggle_reaction(&Annotation::new(event_id.to_owned(), "👍".to_owned())).await.unwrap();
+
+    // First toggle (local echo).
+    {
+        assert_let!(Some(VectorDiff::Set { index: 1, value: item }) = stream.next().await);
+
+        let reactions = item.as_event().unwrap().reactions();
+        assert_eq!(reactions.len(), 1);
+        assert_matches!(
+            &reactions.get("👍").unwrap().get(user_id).unwrap().status,
+            ReactionStatus::LocalToRemote(_)
+        );
+
+        assert!(stream.next().now_or_never().is_none());
+    }
+
+    // We toggle another reaction at the same time…
+    timeline.toggle_reaction(&Annotation::new(event_id.to_owned(), "🥰".to_owned())).await.unwrap();
+
+    {
+        assert_let!(Some(VectorDiff::Set { index: 1, value: item }) = stream.next().await);
+
+        let reactions = item.as_event().unwrap().reactions();
+        assert_eq!(reactions.len(), 2);
+        assert_matches!(
+            &reactions.get("👍").unwrap().get(user_id).unwrap().status,
+            ReactionStatus::LocalToRemote(_)
+        );
+        assert_matches!(
+            &reactions.get("🥰").unwrap().get(user_id).unwrap().status,
+            ReactionStatus::LocalToRemote(_)
+        );
+
+        assert!(stream.next().now_or_never().is_none());
+    }
+
+    // Then we remove the first one; because it was being sent, it should lead to a
+    // redaction event.
+    timeline.toggle_reaction(&Annotation::new(event_id.to_owned(), "👍".to_owned())).await.unwrap();
+
+    {
+        assert_let!(Some(VectorDiff::Set { index: 1, value: item }) = stream.next().await);
+
+        let reactions = item.as_event().unwrap().reactions();
+        assert_eq!(reactions.len(), 1);
+        assert_matches!(
+            &reactions.get("🥰").unwrap().get(user_id).unwrap().status,
+            ReactionStatus::LocalToRemote(_)
+        );
+
+        assert!(stream.next().now_or_never().is_none());
+    }
+
+    // But because the first one was being sent, this one won't and the local echo
+    // could be discarded.
+    timeline.toggle_reaction(&Annotation::new(event_id.to_owned(), "🥰".to_owned())).await.unwrap();
+
+    {
+        assert_let!(Some(VectorDiff::Set { index: 1, value: item }) = stream.next().await);
+
+        let reactions = item.as_event().unwrap().reactions();
+        assert!(reactions.is_empty());
+
+        assert!(stream.next().now_or_never().is_none());
+    }
+
+    // In a real-world setup with a background sync, the reaction may flash to the
+    // user, because the sync may return the reaction event, and later the
+    // redaction of the reaction. In our case, we're done here.
+
+    tokio::time::sleep(Duration::from_millis(300)).await;
+    assert!(stream.next().now_or_never().is_none());
+}