OSX: On Retina display button icon is blurry

#include <QMainWindow>
#include <QApplication>
#include <QtWidgets>

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
    QApplication a(argc, argv);

    QPixmap pix("/tmp/finder.png");

    QIcon icon(pix);

    QToolBar* toolBar = new QToolBar();
    QToolButton* toolButton = new QToolButton();
    toolButton->setIcon(icon);
    toolButton->setCheckable(true);
    toolBar->addWidget(toolButton);

    QMainWindow w;
    w.addToolBar(toolBar);
    w.show();

    toolButton->setChecked(true);

    return a.exec();
}