In the cited work, the authors presented mass spectra, valence photoelectron spectra and calculations of the electronic structure of proline. They claim that several previous photoelectron spectra are invalid because they were influenced by thermal decomposition of the sample. We present photoionization mass spectra of proline as a function of temperature and show that thermal decomposition does not occur in the apparatus and at the temperatures used in our previous work. These spectra are consistent with other published spectra. The conformer populations calculated by these authors, far from contradicting previous interpretations of valence band spectra, are surprisingly consistent with them. (C) 2014 Elsevier B.V. All rights reserved.