  We discuss the effect of kinetic energy of the relative motion becoming
spurious for separate fragments on the selfconsistent mean-field fission
barriers. The treatment of the relative motion in the cluster model is
contrasted with the necessity of a simpler and approximate approach in the
mean-field theory. A scheme of the energy correction to the Hartree-Fock is
proposed. The results obtained with the effective Skyrme interaction SLy6 show
that the correction, previously estimated as $\sim$ 8 MeV in $A=70-100$ nuclei,
amounts to 4 MeV in the medium heavy nucleus $^{198}$Hg and to null in
$^{238}$U. However, the corrected barrier implies a shorter fission half-life
of the latter nucleus. The same effect is expected to lower barriers for
multipartition (i.e. ternary fission, etc) and make hyperdeformed minima less
stable.
