diff --git a/tryton/gui/window/view_form/model/group.py b/tryton/gui/window/view_form/model/group.py
index bb4292180a..67716758fb 100644
--- a/tryton/gui/window/view_form/model/group.py
+++ b/tryton/gui/window/view_form/model/group.py
@@ -44,7 +44,7 @@ class Group(SignalEvent, list):
     @property
     def readonly(self):
         # Must skip res.user for Preference windows
-        if (self._context.get('_datetime')
+        if (self.context.get('_datetime')
                 or (not (MODELACCESS[self.model_name]['write']
                         or MODELACCESS[self.model_name]['create'])
                     and not self.skip_model_access)):