diff --git a/bin/osv/orm.py b/bin/osv/orm.py
index 789d2fa27f8..3fdaddfa92c 100644
--- a/bin/osv/orm.py
+++ b/bin/osv/orm.py
@@ -635,7 +635,7 @@ class orm_template(object):
 			fun, msg, fields = constraint
 			if not fun(self, cr, uid, ids):
 				field_error += fields
-				field_err_str.append( trans._get_source(cr, uid, self._name, 'constraint', lng, source=msg) )
+				field_err_str.append( trans._get_source(cr, uid, self._name, 'constraint', lng, source=msg) or msg )
 		if len(field_err_str):
 			cr.rollback()
 			raise except_orm('ValidateError', ('\n'.join(field_err_str), ','.join(field_error)))