Cannot make a QMessageBox resizable

I was trying to put a lot of text into a QMessageBox detailedText property. However the dialog size was too small to easily read all the text, so I wanted to make the message box resizable. I could not get this to work and had to implement my own 'report dialog' instead.

I expected calling setSizeGripEnabled(true) on a QMessageBox to not just display a size grip but actually make the dialog resizable. It did not.
I also tried various calls to setMaximumSize/setSizePolicy and even resize() but nothing would make the
message box resizable - this was using setDetailedText() so that the message box was to some extent managing its own size when the details were hidden/shown.

Instead I had a non-resizable message box that was too small to read the detailedText correctly.

My suggestion is to either make the QMessageBox resizable OR remove the setSizeGripEnabled() and make it clear in the documentation that the message box is not resizable as I wasted many hours trying to make it work before giving up and writing my own dialog in far less time.