M300 ignores frequency, listens to duration...

OK, I’ve got Marlin RCBugFix working on both my Taz5’s now and the only outstanding issue I’m having is the buzzer doesn’t sound like it should. This is minor but annoying enough I’d like to fix it… previously I could send M300 commands and make it play appropriate noises… now it makes noises, but it’s always the same tone, only the length changes…

// If you have a speaker that can produce tones, enable it here.
// By default Marlin assumes you have a buzzer with a fixed frequency.
#define SPEAKER

I’d expect that needs uncommented, but when I do that, it doesn’t work at all!