Slick fillRoundRect not drawing anything on screen

Question

Graphics.fillRoundRect() seems not to be working properly, as no Rectangle appears. drawRect() works fine however. I tried:

    g.setColor(new Color(255,255,255));
    g.setBackground(new Color(255,255,255));
    g.setAntiAlias(true);
    g.fillRoundRect(0,0,100,100,25,30);
    g.setAntiAlias(false);

as well as

    g.setColor(new Color(255,255,255));
    g.setBackground(new Color(255,255,255));
    g.fillRoundRect(0,0,100,100,25,30);

The only thing that worked, was using drawRect, but that of course doesn't fill it in.