diff --git a/packages/polka/index.d.ts b/packages/polka/index.d.ts
index fbee9bf..1eb4d18 100644
--- a/packages/polka/index.d.ts
+++ b/packages/polka/index.d.ts
@@ -4,7 +4,7 @@ import type { ParsedURL } from '@polka/url';
 import type Trouter from 'trouter';
 
 type Promisable<T> = Promise<T> | T;
-type ListenCallback = () => Promisable<void>;
+type ListenCallback = (err?: string | IError) => Promisable<void>;
 
 export interface IError extends Error {
 	code?: number;