In a recent paper, Chen et al. considered the destabilization of the universal mode in a tokamak by electron-ion collisions. In their analysis, a large-aspect-ratio tokamak with circular concentric flux surfaces was assumed and collisions were modelled by a parallel friction term in the electron equation of motion. Attention was focused on perturbations with large toroidal mode numbers, and use was made of the simplifying ballooning-mode representation. The particular form of the ballooning-mode formalism used, however, necessitated a truncated Taylor series in ωde/ω (to be defined later) and, thereby, resulted in an approximate eigenmode equation.