[Gtk-sharp-list] Label.Justify question

[eniac@sdf-eu.org]

I've created 2labels and I try to Justify them by doing

label1.Justify = Gtk.Justify.Left
label2.Justify = Gtk.Justify.Right

But when compiling I always get this error:

mylabel.cs(13) error CS0103: The name `Gtk.Justify.Left' could not be 
found in `mylabel'