C# 窗口窗体中的绘制点

Visual Studio 说有一个未处理的 OverflowException

//draws the point.
public void Draw(Graphics g)
{
    float radius = 3; //radius of the circle which describes the point.
    // draws the circle of the point, with parameters of the square which bounds the circle.
    g.DrawEllipse(new Pen(Color.Black, 6F), float.Parse((this.X - radius).ToString()), float.Parse((this.Y - radius).ToString()), 2 * radius, 2 * radius);
}