diff --git a/tryton/modules/stock/message.xml b/tryton/modules/stock/message.xml
index ac05419240..dcae4e4632 100644
--- a/tryton/modules/stock/message.xml
+++ b/tryton/modules/stock/message.xml
@@ -16,6 +16,9 @@ You must use the "Modify Cost Price" wizard.</field>
         <record model="ir.message" id="msg_invalid_cost_price">
             <field name="text">Invalid cost price "%(cost_price)s" for product "%(product)s" with exception "%(exception)s".</field>
         </record>
+        <record model="ir.message" id="msg_invalid_cost_price_not_number">
+            <field name="text">The value "%(value)s" of "%(cost_price)s" for product "%(product)s" is not a number.</field>
+        </record>
         <record model="ir.message" id="msg_location_invalid_type_for_moves">
             <field name="text">You cannot change the type of location "%(location)s" to "%(type)s"
 because the type does not support moves and location has existing moves.</field>
diff --git a/tryton/modules/stock/product.py b/tryton/modules/stock/product.py
index e4da113ef3..96a9fac580 100644
--- a/tryton/modules/stock/product.py
+++ b/tryton/modules/stock/product.py
@@ -6,7 +6,7 @@ from collections import defaultdict
 from copy import deepcopy
 from decimal import Decimal

-from simpleeval import simple_eval
+from simpleeval import InvalidExpression, simple_eval
 from sql import Literal, Select, Window, With
 from sql.aggregate import Max, Sum
 from sql.conditionals import Case, Coalesce
@@ -1233,22 +1233,27 @@ class CostPriceRevision(ModelSQL, ModifyCostPriceStart):
         if field_names and 'cost_price' not in field_names:
             return
         for revision in revisions:
-            try:
-                if not isinstance(
-                        revision.get_cost_price(Decimal(0)), Decimal):
-                    raise ValueError
-            except Exception as exception:
-                product = revision.product or revision.template
-                raise ProductCostPriceError(
-                    gettext('stock.msg_invalid_cost_price',
-                        cost_price=revision.cost_price,
-                        product=product.rec_name,
-                        exception=exception)) from exception
+            revision.get_cost_price(Decimal(0))

     def get_cost_price(self, cost_price, **context):
         context.setdefault('names', {})['cost_price'] = cost_price
         context.setdefault('functions', {})['Decimal'] = Decimal
-        return simple_eval(decistmt(self.cost_price), **context)
+        try:
+            amount = simple_eval(decistmt(self.cost_price), **context)
+        except (InvalidExpression, SyntaxError) as exception:
+            product = self.product or self.template
+            raise ProductCostPriceError(
+                gettext('stock.msg_invalid_cost_price',
+                    cost_price=self.cost_price,
+                    product=product.rec_name,
+                    exception=exception)) from exception
+        if not isinstance(amount, Decimal):
+            raise ProductCostPriceError(
+                gettext('stock.msg_invalid_cost_price_not_number',
+                    value=amount,
+                    cost_price=self.cost_price,
+                    product=product.rec_name))
+        return amount

     @classmethod
     def _get_for_product_domain(cls):