Have a mc rotate on itself

Hi everybody,

I have a mc that I need to be rotating on itself every other frame, so I did something like this on the MC :

[AS]
onClipEvent(enterFrame)
{
this._rotation += 8;
}
[/AS]

The thing is that it rotates aroung its upper left corner. So how do I specify that I want it to rotate from the middle of the MC ?

Once again, thanks in advance