ASSERT failure in QShortcutMap::find: "New sequence to find identical to previous"

class MainWindow : public QWidget
{
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
protected:

};

MainWindow::MainWindow(QWidget *parent) :
    QWidget(parent)
{
    QVBoxLayout *layout = new QVBoxLayout(this);

    QPushButton *fiveButton = new QPushButton("5");

    QTextEdit *edit = new QTextEdit;

    layout->addWidget(fiveButton);
    layout->addWidget(edit);

    fiveButton->setShortcut(QKeySequence(Qt::Key_5));
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    MainWindow w;
    w.show();

    return a.exec();
}