New Android Toolbar: How to hide the overflow menu icon?

I just created an app including the new Android toolbar. My problem is: How would I hide this overflow menu icon/button: http://prntscr.com/62mmus ? I already tried this, but it's not working:

        Toolbar mToolbar = (Toolbar) findViewById(R.id.toolbar);
        mToolbar.hideOverflowMenu();

Just use:

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
        return false;
}