Rounded corners in Qt Webengine

[Shwoomple]

How do I add rounded corners to a QWebEngineView in Qt Widgets? I have tried using a mask like so

void Tab::resizeEvent(QResizeEvent *event){
    QPainterPath path;
    path.addRoundedRect(rect(), 10, 10);
    this->setMask(path.toFillPolygon().toPolygon());
}

This does add rounded corners, but also causes them to be jagged

I get better results using QML, but would prefer to continue using Qt Widgets if possible. Thank you.