It is shown that an expansion of the configurational energy in powers of density allows correcting the critical behavior of Ono-Kondo theory for multilayer adsorption. The proposed approach results in a new equation relating densities in each layer with density in the bulk. This equation predicts spinodals and binodals which are in excellent agreement with the exact phase diagram for a two-dimensional system and with the phase diagram known from Monte Carlo simulations for a three-dimensional system.