diff --git a/index.ts b/index.ts
index 67ba4c1..70203e8 100644
--- a/index.ts
+++ b/index.ts
@@ -202,7 +202,7 @@ export class AppStoreServerAPIClient {
     private keyId: string
     private signingKey: string
     private bundleId: string
-    private urlBase: string
+    protected urlBase: string
 
     /**
      * Create an App Store Server API client