diff --git a/configuration.py b/configuration.py
index d1a5513..1ad43b1 100644
--- a/configuration.py
+++ b/configuration.py
@@ -5,10 +5,10 @@ from trytond.model import fields
 from trytond.pool import PoolMeta
 
 __all__ = ['Configuration']
-__metaclass__ = PoolMeta
 
 
 class Configuration:
+    __metaclass__ = PoolMeta
     __name__ = 'sale.configuration'
     enough_stock_qty = fields.Property(fields.Selection([
         ('quantity', 'Quantity'),
diff --git a/sale.py b/sale.py
index 5fbea2f..688401b 100644
--- a/sale.py
+++ b/sale.py
@@ -5,11 +5,11 @@ from trytond.pool import Pool, PoolMeta
 from trytond.transaction import Transaction
 
 __all__ = ['Sale']
-__metaclass__ = PoolMeta
 PRODUCT_TYPES = ['goods']
 
 
 class Sale:
+    __metaclass__ = PoolMeta
     __name__ = 'sale.sale'
 
     @classmethod