A different treatment of the electronic contribution to the in-plane thermal conductivity of high-T-c superconductors than in Graf et al. [Phys. Rev. B 53, 15 147 (1996)] leads to a nonconventional T-2 dependence of the electron-impurity contribution in contrast to the predicted linear dependence of Graf et al. In fact, taking into account both electron-impurity-phonon scattering leads to a nontrivial T-beta dependence as found experimentally in various high-T-c materials, where beta results from different T-dependent contributions as well as the values of the impurity fraction in the sample N and the in-plane transport electron-phonon coupling constant of the material lambda(ab).