diff --git a/index.d.ts b/index.d.ts
index b59a08f..888b4a8 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -58,6 +58,8 @@ declare namespace Router {
     searchParams: { [k: string]: string }
   ) => any;
 
+  type Done = (err: Error | null, result: any) => void;
+
   interface ConstraintStrategy<V extends HTTPVersion, T = string> {
     name: string,
     mustMatchWhenDerived?: boolean,
@@ -160,7 +162,8 @@ declare namespace Router {
     lookup<Context>(
       req: Req<V>,
       res: Res<V>,
-      ctx?: Context
+      ctx?: Context | Done,
+      done?: Done
     ): any;
 
     find(
diff --git a/test/types/router.test-d.ts b/test/types/router.test-d.ts
index d00f2af..ee7bfeb 100644
--- a/test/types/router.test-d.ts
+++ b/test/types/router.test-d.ts
@@ -7,10 +7,12 @@ let http1Req!: IncomingMessage;
 let http1Res!: ServerResponse;
 let http2Req!: Http2ServerRequest;
 let http2Res!: Http2ServerResponse;
+let ctx!: { req: IncomingMessage; res: ServerResponse };
+let done!: (err: Error | null, result: any) => void;
 
 // HTTP1
 {
-  let handler: Router.Handler<Router.HTTPVersion.V1>
+  let handler!: Router.Handler<Router.HTTPVersion.V1>
   const router = Router({
     ignoreTrailingSlash: true,
     ignoreDuplicateSlashes: true,
@@ -52,6 +54,8 @@ let http2Res!: Http2ServerResponse;
   expectType<void>(router.off(['GET', 'POST'], '/'))
 
   expectType<any>(router.lookup(http1Req, http1Res))
+  expectType<any>(router.lookup(http1Req, http1Res, done));
+  expectType<any>(router.lookup(http1Req, http1Res, ctx, done));
   expectType<Router.FindResult<Router.HTTPVersion.V1> | null>(router.find('GET', '/'))
   expectType<Router.FindResult<Router.HTTPVersion.V1> | null>(router.find('GET', '/', {}))
   expectType<Router.FindResult<Router.HTTPVersion.V1> | null>(router.find('GET', '/', {version: '1.0.0'}))
@@ -86,7 +90,7 @@ let http2Res!: Http2ServerResponse;
     }
   }
 
-  let handler: Router.Handler<Router.HTTPVersion.V2>
+  let handler!: Router.Handler<Router.HTTPVersion.V2>
   const router = Router<Router.HTTPVersion.V2>({
     ignoreTrailingSlash: true,
     ignoreDuplicateSlashes: true,
@@ -117,6 +121,8 @@ let http2Res!: Http2ServerResponse;
   expectType<void>(router.off(['GET', 'POST'], '/'))
 
   expectType<any>(router.lookup(http2Req, http2Res))
+  expectType<any>(router.lookup(http2Req, http2Res, done));
+  expectType<any>(router.lookup(http2Req, http2Res, ctx, done));
   expectType<Router.FindResult<Router.HTTPVersion.V2> | null>(router.find('GET', '/', {}))
   expectType<Router.FindResult<Router.HTTPVersion.V2> | null>(router.find('GET', '/', {version: '1.0.0', host: 'fastify.io'}))
 
@@ -127,7 +133,7 @@ let http2Res!: Http2ServerResponse;
 
 // Custom Constraint
 {
-  let handler: Router.Handler<Router.HTTPVersion.V1>
+  let handler!: Router.Handler<Router.HTTPVersion.V1>
 
   interface AcceptAndContentType { accept?: string, contentType?: string }