It is shown that the differential equation of Smagala and Fawcett [T.G. Smagala, W.R. Fawcett, J. Electroanal. Chem. 597 (2006) 43] for an electrified interface is similar, but not equivalent, to the hypernetted chain approximation integral equation. Nonetheless, their differential equation is of interest and is an improvement over the Poisson-Boltzmann approximation of Gouy and Chapman and may lead to further improvements. (c) 2006 Elsevier B.V. All rights reserved.