diff --git a/socket.io/socket.io.d.ts b/socket.io/socket.io.d.ts
index b6aad32931..b1db7515fa 100644
--- a/socket.io/socket.io.d.ts
+++ b/socket.io/socket.io.d.ts
@@ -27,10 +27,10 @@ declare module SocketIO {
         adapter(v: any): Server;
         origins(v: string): Server;
         sockets: Namespace;
-        attach(srv: any, opts: any): Server;
-        attach(port: number, opts: any): Server;
-        listen(srv: any, opts: any): Server;
-        listen(port: number, opts: any): Server;
+        attach(srv: any, opts?: any): Server;
+        attach(port: number, opts?: any): Server;
+        listen(srv: any, opts?: any): Server;
+        listen(port: number, opts?: any): Server;
         bind(srv: any): Server;
         onconnection(socket: any): Server;
         of(nsp: string): Namespace;