Compile Fails With Recent Vala Versions (2.2+)

Can't compile on new versions of Vala (and I'm sure this error is just one example of many issues pointing out that an update to the source code is in order, if this project is actually being maintained, and to survive):

applet.vala:291.23-291.29: error: `Timeout' is an ambiguous reference between `GLib.Timeout' and `Gtk.Timeout'
      this.timer_id = Timeout.add (300, this.on_timer_tick);