diff --git a/trytond/trytond/modules/stock/product.py b/trytond/trytond/modules/stock/product.py
index bbe41a5..169f46e 100644
--- a/trytond/trytond/modules/stock/product.py
+++ b/trytond/trytond/modules/stock/product.py
@@ -16,6 +16,7 @@ from trytond.pyson import PYSONEncoder, Eval, Or
 from trytond.transaction import Transaction
 from trytond.pool import Pool, PoolMeta
 from trytond.tools import grouped_slice
+from trytond.exceptions import UserError

 from trytond.modules.product import TemplateFunction
 from .move import StockMixin
@@ -126,11 +127,14 @@ class Product(StockMixin, object):
         with Transaction().set_context(context):
             for product in cls.browse(products):
                 # The date could be before the product creation
-                if not isinstance(product.cost_price, Decimal):
+                try:
+                    if not isinstance(product.cost_price, Decimal):
+                        cost_values[product.id] = None
+                    else:
+                        cost_values[product.id] = (Decimal(str(product.quantity))
+                            * product.cost_price)
+                except UserError:
                     cost_values[product.id] = None
-                else:
-                    cost_values[product.id] = (Decimal(str(product.quantity))
-                        * product.cost_price)
         return cost_values

     @classmethod