diff --git a/openerp/addons/base/ir/ir_fields.py b/openerp/addons/base/ir/ir_fields.py
index 65d4a786178..05aa6782e9c 100644
--- a/openerp/addons/base/ir/ir_fields.py
+++ b/openerp/addons/base/ir/ir_fields.py
@@ -127,7 +127,8 @@ class ir_fields_converter(orm.Model):
             return value, []
         except ValueError:
             raise ValueError(
-                _(u"'%s' does not seem to be a valid date for field '%%(field)s'") % value)
+                _(u"'%s' does not seem to be a valid date for field '%%(field)s'. Use the format '%s'") %
+                    (value, u"2012-12-31"))
 
     def _str_to_datetime(self, cr, uid, model, column, value, context=None):
         try:
@@ -135,7 +136,8 @@ class ir_fields_converter(orm.Model):
             return value, []
         except ValueError:
             raise ValueError(
-                _(u"'%s' does not seem to be a valid datetime for field '%%(field)s'") % value)
+                _(u"'%s' does not seem to be a valid datetime for field '%%(field)s'. Use the format '%s'") %
+                    (value, u"2012-12-31 23:59:59"))
 
     def _get_translations(self, cr, uid, types, src, context):
         types = tuple(types)
diff --git a/openerp/tests/addons/test_impex/tests/test_load.py b/openerp/tests/addons/test_impex/tests/test_load.py
index 65c4b6e9e57..8bfcd20f4f3 100644
--- a/openerp/tests/addons/test_impex/tests/test_load.py
+++ b/openerp/tests/addons/test_impex/tests/test_load.py
@@ -1008,7 +1008,7 @@ class test_date(ImporterCase):
         result = self.import_(['value'], [['not really a date']])
         self.assertEqual(result['messages'], [
             message(u"'not really a date' does not seem to be a valid date "
-                    u"for field 'unknown'")])
+                    u"for field 'unknown'. Use the format '2012-12-31'")])
         self.assertIs(result['ids'], False)
 
 class test_datetime(ImporterCase):
@@ -1028,7 +1028,8 @@ class test_datetime(ImporterCase):
         result = self.import_(['value'], [['not really a datetime']])
         self.assertEqual(result['messages'], [
             message(u"'not really a datetime' does not seem to be a valid "
-                    u"datetime for field 'unknown'")])
+                    u"datetime for field 'unknown'. Use the format "
+                    u"'2012-12-31 23:59:59'")])
         self.assertIs(result['ids'], False)
 
 # function, related, reference: written to db as-is...