diff --git a/packages/in_app_purchase/lib/src/in_app_purchase/purchase_details.dart b/packages/in_app_purchase/lib/src/in_app_purchase/purchase_details.dart
index 2321bd00abdc..fe66e634e11b 100644
--- a/packages/in_app_purchase/lib/src/in_app_purchase/purchase_details.dart
+++ b/packages/in_app_purchase/lib/src/in_app_purchase/purchase_details.dart
@@ -79,7 +79,8 @@ class PurchaseParam {
   PurchaseParam(
       {@required this.productDetails,
       this.applicationUserName,
-      this.sandboxTesting});
+      this.sandboxTesting = false})
+      : assert(sandboxTesting != null);
 
   /// The product to create payment for.
   ///