diff --git a/express-serve-static-core/index.d.ts b/express-serve-static-core/index.d.ts
index 42f1a535f7..a4ce9612e7 100644
--- a/express-serve-static-core/index.d.ts
+++ b/express-serve-static-core/index.d.ts
@@ -848,6 +848,8 @@ interface Response extends http.ServerResponse, Express.Response {
      *
      */
     vary(field: string): Response;
+
+    app: Application;
 }
 
 interface Handler extends RequestHandler { }