  In a recent preprint Cheon and Cheoun have derived from a chiral model an
additional term, not usually appearing in the standard matrix element for
radiative muon capture. Using that term they generate a large correction to the
RMC spectrum which tends to resolve the problem caused by the too large value
of $g_P$ found in the TRIUMF RMC experiment. In this comment we observe first
that their extra term leads to an amplitude which is not gauge invariant and
second that such a term should be present, in a gauge invariant way, in an
earlier full chiral perturbation theory calculation, which however found
negligible differences from the standard approach.
