diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 5fe7b363..b2492784 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -562,7 +562,7 @@ export interface FileNode {
 }
 
 export interface EventDoc {
-    sender: string;
+    ack: string[];
     event: number | string;
     payload: string;
     expire: Date;
diff --git a/packages/hydrooj/src/model/task.ts b/packages/hydrooj/src/model/task.ts
index 6185e45e..a69a5d00 100644
--- a/packages/hydrooj/src/model/task.ts
+++ b/packages/hydrooj/src/model/task.ts
@@ -2,7 +2,7 @@ import { hostname } from 'os';
 import moment from 'moment-timezone';
 import { FilterQuery, ObjectID } from 'mongodb';
 import { sleep } from '@hydrooj/utils/lib/utils';
-import { BaseService, Task } from '../interface';
+import { BaseService, EventDoc, Task } from '../interface';
 import { Logger } from '../logger';
 import * as bus from '../service/bus';
 import db from '../service/db';
@@ -161,18 +161,35 @@ bus.once('app/started', async () => {
         });
     }
     await collEvent.createIndex({ expire: 1 }, { expireAfterSeconds: 0 });
-    const stream = collEvent.watch([{ $match: { sender: { $ne: id } } }]);
-    stream.on('change', async (change) => {
-        if (change.operationType !== 'insert') return;
-        const doc = change.fullDocument;
+    const stream = collEvent.watch();
+    const handleEvent = async (doc: EventDoc) => {
         const payload = JSON.parse(doc.payload);
         if (process.send) process.send({ type: 'hydro:broadcast', data: { event: doc.event, payload } });
-        if (doc) bus.parallel(doc.event, ...payload);
+        await bus.parallel(doc.event, ...payload);
+    };
+    stream.on('change', async (change) => {
+        if (change.operationType !== 'insert') return;
+        if (change.fullDocument.ack.includes(id)) return;
+        await handleEvent(change.fullDocument);
+    });
+    stream.on('error', async () => {
+        // The $changeStream stage is only supported on replica sets
+        logger.info('No replica set found.');
+        // eslint-disable-next-line no-constant-condition
+        while (true) {
+            // eslint-disable-next-line no-await-in-loop
+            const res = await collEvent.findOneAndUpdate(
+                { ack: { $nin: [id] } },
+                { $push: { ack: id } },
+            );
+            // eslint-disable-next-line no-await-in-loop
+            await (res.value ? handleEvent(res.value) : sleep(500));
+        }
     });
 });
 bus.on('bus/broadcast', (event, payload) => {
     collEvent.insertOne({
-        sender: id,
+        ack: [id],
         event,
         payload: JSON.stringify(payload),
         expire: new Date(Date.now() + 10000),