diff --git a/src/lhisp-oauth-client.t.ts b/src/lhisp-oauth-client.t.ts
index 0fdaf45..38e5dfc 100644
--- a/src/lhisp-oauth-client.t.ts
+++ b/src/lhisp-oauth-client.t.ts
@@ -18,7 +18,7 @@ export interface LhispOauthClientConstructorParams {
   authHeaders?: Headers;
   grantType?: string;
   authContentType?: ContentType;
-  authData: Record<string, string>;
+  authData?: Record<string, string>;
   sendAuthCredentialsOnRequestBody?: boolean;
   formatAccessToken?: (accessToken?: AccessToken) => string;
   debug?: boolean;