diff --git a/category.py b/category.py
index 8b0e843400..613bb655c2 100644
--- a/category.py
+++ b/category.py
@@ -22,9 +22,11 @@ class Category(OSV):
     def __init__(self):
         super(Category, self).__init__()
         self._constraints += [
-            ('check_recursion',
-             'Error! You can not create recursive categories.', ['parent'])
+            ('check_recursion', 'recursive_categories'),
         ]
+        self._error_messages.update({
+            'recursive_categories': 'You can not create recursive categories!',
+        })
         self._order.insert(1, ('name', 'ASC'))
 
     def default_active(self, cursor, user, context=None):
diff --git a/party.py b/party.py
index b7721cf10e..a6a2ee41b6 100644
--- a/party.py
+++ b/party.py
@@ -97,9 +97,11 @@ class Party(OSV):
              'The code of the party must be unique!')
         ]
         self._constraints += [
-            ('check_vat',
-                'Error! Wrong VAT number.', ['vat_number', 'vat_country']),
+            ('check_vat', 'wrong_vat'),
         ]
+        self._error_messages.update({
+            'wrong_vat': 'Wrong VAT number!',
+        })
         self._order.insert(0, ('name', 'DESC'))
 
     def default_active(self, cursor, user, context=None):