diff --git a/product/ERP5Form/FormBox.py b/product/ERP5Form/FormBox.py
index 9fe5aa79f6996241ed0afe84a886f6335268aa49..1d41a21e43cb44e8ec4fa39f03550748cf7461e1 100644
--- a/product/ERP5Form/FormBox.py
+++ b/product/ERP5Form/FormBox.py
@@ -143,9 +143,10 @@ class FormBoxValidator(Validator.Validator):
   """
   property_names = Validator.Validator.property_names
   message_names = Validator.Validator.message_names + \
-                  ['form_invalidated',]
+                  ['form_invalidated', 'required_not_found']
 
   form_invalidated = "Form invalidated."
+  required_not_found = 'Input is required but no input given.'
 
   def validate(self, field, key, REQUEST):
     # XXX hardcoded acquisition