Clearing Timer That Is An Objects Property

I have an object that has a fade method

Code:
ImageHandler.prototype.fade = function()
{
var oThis = this;

if(// some conditions)
{
window.clearTimeout(oThis.timer);
}


// the this.timer is set to null in the constructor.
this.timer = window.setTimeout(function(){ oThis.fade() }, 150);
}
Problem I have is that the timer is not cleared. The if when the timer should be cleared works fine, so I took it out in this example to minimize the code.

I also tried window.clearTimeout(this.timer) with no luck. Any ideas?