terminal – How do I make the ‘say -v PersonalVoice’ command save output to a file?

Thanks to this answer, I was able to grant permission to the Terminal and iTerm2 apps to use a Personal Voice with the ‘say’ command; e.g.

say -v MyVoice "Hello, world!"

The say command has a number of options, including -o output.aiff which writes the spoken text to an AIFF file.

say -v Alex -o test.aiff "Hello world"
afplay test.aiff

However, I can’t get it to work for my personal voice:

say -v MyVoice -o test.aiff "Hello world"
afplay test.aiff

produces nothing but a moment of silence.

It seems most likely, judging from the number of loose ends I’ve hit playing with the Personal Voice feature, that this is a bug, but perhaps I’ve overlooked something.