diff --git a/tryton/gui/window/view_form/widget_search/calendar.py b/tryton/gui/window/view_form/widget_search/calendar.py
index 0a0b59c6d6..1cfc8a1ec8 100644
--- a/tryton/gui/window/view_form/widget_search/calendar.py
+++ b/tryton/gui/window/view_form/widget_search/calendar.py
@@ -122,7 +122,7 @@ class Calendar(Interface):
         win.destroy()
 
     def clear(self):
-        self.value = ''
+        self.value = ('', '')
 
     def sig_activate(self, fct):
         self.entry1.connect_after('activate', fct)