diff --git a/socket.io/socket.io.d.ts b/socket.io/socket.io.d.ts
index 258b573d5..ba7a5ba70 100644
--- a/socket.io/socket.io.d.ts
+++ b/socket.io/socket.io.d.ts
@@ -46,6 +46,7 @@ declare module SocketIO {
         name: string;
         connected: { [id: string]: Socket };
         use(fn: Function): Namespace;
+        in(room: string): Namespace;
 
         on(event: 'connection', listener: (socket: Socket) => void): Namespace;
         on(event: 'connect', listener: (socket: Socket) => void): Namespace;