diff --git a/index.d.ts b/index.d.ts
index 3a4137f6..7fa3a0d4 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -3928,7 +3928,7 @@ declare class Webhooks {
   public middleware(
     request: http.IncomingMessage,
     response: http.ServerResponse,
-    next: (err?: any) => void
+    next?: (err?: any) => void
   ): void | Promise<void>;
 }