diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 04ab4e805..de35a43f0 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -305,7 +305,6 @@ export interface DomainDoc extends Record<string, any> {
 
 // Message
 export interface MessageDoc {
-    _id: ObjectId,
     from: number,
     to: number,
     content: string,
diff --git a/packages/hydrooj/src/model/message.ts b/packages/hydrooj/src/model/message.ts
index 291a64afd..f43a14d53 100644
--- a/packages/hydrooj/src/model/message.ts
+++ b/packages/hydrooj/src/model/message.ts
@@ -21,11 +21,8 @@ class MessageModel {
         from: number, to: number | number[],
         content: string, flag: number = MessageModel.FLAG_UNREAD,
     ) {
-        const _id = new ObjectId();
         if (!Array.isArray(to)) to = [to];
-        const base = {
-            _id, from, content, flag,
-        };
+        const base = { from, content, flag };
         if (!to.length) return base;
         await MessageModel.coll.insertMany(to.map((t) => ({ ...base, to: t })));
         bus.broadcast('user/message', to, base);