diff --git a/tryton/gui/window/view_form/model/field.py b/tryton/gui/window/view_form/model/field.py
index 158981bd0f..8938df102b 100644
--- a/tryton/gui/window/view_form/model/field.py
+++ b/tryton/gui/window/view_form/model/field.py
@@ -256,6 +256,8 @@ class DateField(CharField):
 
 class TimeField(CharField):
 
+    _default = None
+
     def set_client(self, record, value, force_change=False):
         if not isinstance(value, datetime.time):
             try: