We need to add a child to the button to get the right allocation of the pixbuf. When the button is created without a pixbuf, get_preferred_width/height are called the first time when the widget is allocated and 0x0 size is cached by gtksizerequest. Since the widget doesn't change its size when a pixbuf is set, gtk_widget_queue_resize() always uses the cached values instead of calling get_preferred_width_height() again. So the actual size, based on pixbuf size, is never used. We are overriding the draw() method, so having a child doesn't affect the widget rendering anyway. Taken from gnome-panel commit: 0b8ace11087855d741cdeed97dc839db50319ae8 from: Carlos Garcia Campos <[email protected]>