Getting MouseMoveEvents in Qt

In my program, I'd like to have mouseMoveEvent(QMouseEvent* event) called whenever the mouse moves (even when it's over another window).

Right now, in my mainwindow.cpp file, I have:

void MainWindow::mouseMoveEvent(QMouseEvent* event) {
    qDebug() << QString::number(event->pos().x());
    qDebug() << QString::number(event->pos().y());
}

But this seems to only be called when I click and drag the mouse while over the window of the program itself. I've tried calling

setMouseTracking(true);

in MainWindow's constructor, but this doesn't seem to do anything differently (mouseMoveEvent still is only called when I hold a mouse button down, regardless of where it is). What's the easiest way to track the mouse position globally?