diff --git a/types/express-serve-static-core/index.d.ts b/types/express-serve-static-core/index.d.ts
index cb7de5faea..00597aa17c 100644
--- a/types/express-serve-static-core/index.d.ts
+++ b/types/express-serve-static-core/index.d.ts
@@ -351,7 +351,7 @@ interface Request extends http.IncomingMessage, Express.Request {
         *
         * @param type
         */
-    is(type: string): boolean;
+    is(type: string): string | false;
 
     /**
         * Return the protocol string "http" or "https"