Way to keep ampersand from getting sanitized?

I have an error message with an html character entity in it ( µ/
µ ). My trouble is, rails swaps my & with & - leaving me with
µ getting shown literally in the message rather than a nice,
neat Greek mu: μ.

I should probably add that the error message is set in a validate
routine on a model - via errors.add() - not in view code.

Is there a trick to this? I suppose if worse comes to worse I can
always substitute a 'u' :\

Thanks for any help!