  We study the photon spectrum line-shape of the $J/\psi \to \gamma\eta_c\to
\gamma X$ decay process in a nonrelativistic effective field theory (EFT)
framework of quantum chromodynamics (QCD). We take into account the finite
width of the $\eta_c$ and include $\mathcal{O}(v^2)$ corrections. We observe
that the photon spectrum line-shape is divergent at large energies due to
polynomially and logarithmically divergent terms, that upon integration over
the photon energies in Dimensional Regularization (DR) produce no contribution
or can be renormalized. We propose to subtract these divergences at the
line-shape level in a manner consistent with the calculation of the width in DR
and $\overline{\hbox{MS}}$ scheme. We analyze CLEO's data with the proposed
subtracted line-shape and find good agreement between the theoretical
prediction and the experimental result.
