  In the article by Ma~\emph{et al.}~[Phys.~Rev.~A {\bf 94}, 052709 (2016)],
$\gamma$-ray spectra for positron annihilation on molecules were calculated in
the independent-particle approximation with the positron wavefunction set to
unity. Based on comparisons with experimental data they concluded that inner
valence electrons play a dominant role in positron annihilation. These
conclusions are incorrect and resulted from fallacious analysis that ignored
the known effect of the positron wavefunction on the spectra.
