The traditional version of solution diffusion imperfections (SDI) model does not take into account solute diffusion through imperfections. Although the mechanism of transport through imperfections is a non-separative viscous flow, the solute concentration at the exit of an imperfection is decreased due to solute diffusion along the membrane towards the surrounding perfect regions, hence, solute diffusion through imperfections. The SDI model was revised by including this phenomenon in it. It was found that the plots in the (1/R, 1/J(v)) coordinates become non-linear. Small and numerous imperfections produce larger deviations from linearity than large and scarce ones. The non-linearity may give rise to errors in extrapolation to the limiting rejection.