diff --git a/tryton/gui/window/view_form/view/widget_parse.py b/tryton/gui/window/view_form/view/widget_parse.py
index a8b27e125c..deff91f8cf 100644
--- a/tryton/gui/window/view_form/view/widget_parse.py
+++ b/tryton/gui/window/view_form/view/widget_parse.py
@@ -42,5 +42,5 @@ class WidgetParse(ParserInterface):
                 widget = res
                 break
             else:
-                pass
+                raise Exception('Unknow view mode: %s' % node.localName)
         return widget