diff --git a/index.d.ts b/index.d.ts
index 250191e3bd..74b2acd2cc 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -62,8 +62,8 @@ export interface AxiosRequestConfig {
   onUploadProgress?: (progressEvent: ProgressEvent) => void;
   onDownloadProgress?: (progressEvent: ProgressEvent) => void;
   maxContentLength?: number;
+  validateStatus?: ((status: number) => boolean | null);
   maxBodyLength?: number;
-  validateStatus?: (status: number) => boolean;
   maxRedirects?: number;
   socketPath?: string | null;
   httpAgent?: any;