diff --git a/types/index.d.ts b/types/index.d.ts
index 4fd08c5..45fb206 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -76,7 +76,7 @@ export interface Context {
 
 export type ResponseInterceptor = (response: Response, options: RequestOptionsInit) => Response | Promise<Response>;
 
-export type OnionMiddleware = (ctx: Context, next: () => void) => void;
+export type OnionMiddleware = (ctx: Context, next: () => Promise<void>) => void;
 export type OnionOptions = { global?: boolean; core?: boolean; defaultInstance?: boolean };
 
 export interface RequestMethod<R = false> {