diff --git a/tryton/gui/window/view_form/model/record.py b/tryton/gui/window/view_form/model/record.py
index 5b08b45406..23e0678329 100644
--- a/tryton/gui/window/view_form/model/record.py
+++ b/tryton/gui/window/view_form/model/record.py
@@ -42,6 +42,9 @@ class EvalEnvironment(dict):
 
     __repr__ = __str__
 
+    def __contains__(self, item):
+        return item in self.parent.mgroup.mfields
+
 
 class ModelRecord(SignalEvent):