diff --git a/index.d.ts b/index.d.ts
index 94b076c..6a83f60 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -241,6 +241,12 @@ export class Axios {
 export interface AxiosInstance extends Axios {
   (config: AxiosRequestConfig): AxiosPromise;
   (url: string, config?: AxiosRequestConfig): AxiosPromise;
+
+  defaults: Omit<AxiosDefaults, 'headers'> & {
+    headers: HeadersDefaults & {
+      [key: string]: string | number | boolean | undefined
+    }
+  };
 }
 
 export interface GenericFormData {
diff --git a/test/typescript/axios.ts b/test/typescript/axios.ts
index 7c304de..66b6b3d 100644
--- a/test/typescript/axios.ts
+++ b/test/typescript/axios.ts
@@ -251,6 +251,8 @@ instance1.post('/user', { foo: 'bar' }, { headers: { 'X-FOO': 'bar' } })
 
 // Defaults
 
+axios.defaults.headers['X-FOO'];
+
 axios.defaults.baseURL = 'https://api.example.com/';
 axios.defaults.headers.common['Authorization'] = 'token';
 axios.defaults.headers.post['X-FOO'] = 'bar';