diff --git a/akad/ShopService.py b/akad/ShopService.py
index 9b9039a..a4191a3 100644
--- a/akad/ShopService.py
+++ b/akad/ShopService.py
@@ -38,7 +38,7 @@ def buyFreeProduct(self, receiverMid, productId, messageTemplate, language, coun
         """
         pass
 
-    def buyMustbuyProduct(self, receiverMid, productId, messageTemplate, language, country, packageId, serialNumber):
+    def buyMustbuyProduct(self, receiverMid, productId, messageTemplate, language, country, packageId, serialNumber, size):
         """
         Parameters:
          - receiverMid
@@ -48,6 +48,7 @@ def buyMustbuyProduct(self, receiverMid, productId, messageTemplate, language, c
          - country
          - packageId
          - serialNumber
+         - size
         """
         pass