diff --git a/CHANGELOG.md b/CHANGELOG.md
index c35aa3679f19..03461956c0d1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,9 @@
 - Fix: 招待コードの発行可能な残り数算出に使用すべきロールポリシーの値が違う問題を修正  
   (Cherry-picked from https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/706)
 
+### Misskey.js
+- Fix: Stream初期化時、別途WebSocketを指定する場合の型定義を修正
+
 ## 2024.10.1
 
 ### Note
diff --git a/packages/backend/test-federation/test/utils.ts b/packages/backend/test-federation/test/utils.ts
index 483bf4b254cc..093277cdb498 100644
--- a/packages/backend/test-federation/test/utils.ts
+++ b/packages/backend/test-federation/test/utils.ts
@@ -232,7 +232,6 @@ export async function isFired<C extends keyof Misskey.Channels, T extends keyof
 	params?: Misskey.Channels[C]['params'],
 ): Promise<boolean> {
 	return new Promise<boolean>(async (resolve, reject) => {
-		// @ts-expect-error TODO: why?
 		const stream = new Misskey.Stream(`wss://${host}`, { token: user.i }, { WebSocket });
 		const connection = stream.useChannel(channel, params);
 		connection.on(type as any, ((msg: any) => {
@@ -266,7 +265,6 @@ export async function isNoteUpdatedEventFired(
 	cond: (msg: Parameters<Misskey.StreamEvents['noteUpdated']>[0]) => boolean,
 ): Promise<boolean> {
 	return new Promise<boolean>(async (resolve, reject) => {
-		// @ts-expect-error TODO: why?
 		const stream = new Misskey.Stream(`wss://${host}`, { token: user.i }, { WebSocket });
 		stream.send('s', { id: noteId });
 		stream.on('noteUpdated', msg => {
diff --git a/packages/misskey-js/etc/misskey-js.api.md b/packages/misskey-js/etc/misskey-js.api.md
index 72c236373d03..61de8b8c7e5c 100644
--- a/packages/misskey-js/etc/misskey-js.api.md
+++ b/packages/misskey-js/etc/misskey-js.api.md
@@ -7,6 +7,7 @@
 import type { AuthenticationResponseJSON } from '@simplewebauthn/types';
 import { EventEmitter } from 'eventemitter3';
 import type { PublicKeyCredentialRequestOptionsJSON } from '@simplewebauthn/types';
+import _ReconnectingWebsocket from 'reconnecting-websocket';
 
 // Warning: (ae-forgotten-export) The symbol "components" needs to be exported by the entry point index.d.ts
 //
@@ -3137,7 +3138,7 @@ export class Stream extends EventEmitter<StreamEvents> implements IStream {
     constructor(origin: string, user: {
         token: string;
     } | null, options?: {
-        WebSocket?: WebSocket;
+        WebSocket?: _ReconnectingWebsocket.Options['WebSocket'];
     });
     // (undocumented)
     close(): void;
diff --git a/packages/misskey-js/src/streaming.ts b/packages/misskey-js/src/streaming.ts
index ffb46c77f6c1..6e34ec150817 100644
--- a/packages/misskey-js/src/streaming.ts
+++ b/packages/misskey-js/src/streaming.ts
@@ -51,7 +51,7 @@ export default class Stream extends EventEmitter<StreamEvents> implements IStrea
 	private idCounter = 0;
 
 	constructor(origin: string, user: { token: string; } | null, options?: {
-		WebSocket?: WebSocket;
+		WebSocket?: _ReconnectingWebsocket.Options['WebSocket'];
 	}) {
 		super();