We use a newly developed method, based on the original Brownian shape motion (BSM) model, to calculate fission-fragment isotopic yields Y(Z, N). Recent measurements of post-neutron isotopic distributions with better than 1 u resolution make it possible, for the first time, to test in detail this model. We here report on the comparison between the measured and the calculated fission fragment average neutron number N N with Z seen in the measurements is also present in the calculations. (C) 2020 The Author(s). Published by Elsevier B.V.