  In the cross section for single-inclusive jet production in electron-nucleon
collisions, the distribution of a quark in an electron appears at
next-to-next-to-leading order. The numerical calculations in Ref. [1] were
carried out using a perturbative approximation for the distribution of a quark
in an electron. We point out that that distribution receives nonperturbative
QCD contributions that invalidate the perturbative approximation. Those
nonperturbative effects enter into cross sections for hard-scattering processes
through resolved-electron contributions and can be taken into account by
determining the distribution of a quark in an electron phenomenologically.
