locally installed TTF overrides Google fonts

Question

I'm using the Ubuntu font from Google Fonts:

<link href='http://fonts.googleapis.com/css?family=Ubuntu:300,400,300italic,400italic,500,500italic,700,700italic' rel='stylesheet' type='text/css' />

My stylesheet:

body {
    font-family: 'ubuntu',arial;
}

It works, but if install a font with the same name (Ubuntu), it overrides the one from Google Fonts.

Is it possible to force the browser to use the one from Google Fonts?