diff --git a/tryton/gui/window/form.py b/tryton/gui/window/form.py
index e86bba6976..1bfda784ff 100644
--- a/tryton/gui/window/form.py
+++ b/tryton/gui/window/form.py
@@ -608,7 +608,7 @@ class Form(SignalEvent, TabContent):
 
     def _popup_menu_selected(self, menuitem, togglebutton, action, keyword):
         event = gtk.get_current_event()
-        if event.button == 1:
+        if not hasattr(event, 'button') or event.button == 1:
             hide = not bool(event.state
                 & (gtk.gdk.CONTROL_MASK | gtk.gdk.MOD1_MASK))
         else: