diff --git a/index.d.ts b/index.d.ts
index 188895d2cd..0993b6c1aa 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,5 +1,5 @@
 export interface AxiosTransformer {
-  (data: any): any;
+  (data: any, headers?: any): any;
 }
 
 export interface AxiosAdapter {