diff --git a/openerp/addons/base/ir/ir_fields.py b/openerp/addons/base/ir/ir_fields.py
index e714e6c11f9..1c14fdb3c4d 100644
--- a/openerp/addons/base/ir/ir_fields.py
+++ b/openerp/addons/base/ir/ir_fields.py
@@ -297,7 +297,7 @@ class ir_fields_converter(orm.Model):
                 cr, uid, model, column, subfield, reference, context=context)
             ids.append(id)
             warnings.extend(ws)
-        return REPLACE_WITH(ids), warnings
+        return [REPLACE_WITH(ids)], warnings
 
     def _str_to_one2many(self, cr, uid, model, column, records, context=None):
         commands = []