diff --git a/product.py b/product.py
index e40ba4b..832be27 100644
--- a/product.py
+++ b/product.py
@@ -11,12 +11,22 @@ class Product:
     'Product Product'
     __name__ = 'product.product'
 
+    @classmethod
+    def __setup__(cls):
+        super(Product, cls).__setup__()
+        cls._error_messages.update({
+                'purchasable_sequence': 'Configure purchasable sequence'
+                    ' in Product Configuration',
+                })
+
     @classmethod
     def get_purchase_sequence(cls):
         Sequence = Pool().get('ir.sequence')
         Configuration = Pool().get('product.configuration')
 
         config = Configuration(1)
+        if not config.purchasable_sequence:
+            cls.raise_user_error('purchasable_sequence')
         code = Sequence.get_id(config.purchasable_sequence.id)
         return code