diff --git a/lib/paymill/models/checksum.rb b/lib/paymill/models/checksum.rb
index a2333ce..dfe4812 100644
--- a/lib/paymill/models/checksum.rb
+++ b/lib/paymill/models/checksum.rb
@@ -17,7 +17,7 @@ def self.create_with?( incoming_arguments )
 
     def self.allowed_arguments
       [
-        :checksum_type, :amount, :currency, :return_url, :cancel_url, :description,
+        :checksum_type, :checksum_action, :amount, :currency, :return_url, :cancel_url, :description,
         :shipping_address, :billing_address, :items, :shipping_amount, :handling_amount, :client_id,
         :require_reusable_payment, :reusable_payment_description,
         :fee_amount, :fee_payment, :fee_currency, :app_id