We address the question of whether the large-N expansion in pure SUðNÞ gauge theories requires that k-string tensions must have a power series expansion in 1=N 2 , as in the sine law, or whether 1=N contributions are also allowable, as in Casimir scaling. We find that k-string tensions may, in fact, have 1=N corrections, and consistency with the large-N expansion in the open string sector depends crucially on an exact cancellation, which we will prove, among terms involving odd powers of 1=N in particular combinations of Wilson loops. It is shown how these cancellations are fulfilled, and consistency with the large-N expansion achieved, in a concrete example, namely, strong coupling lattice gauge theory with the heat-kernel action. This is a model which has both a 1=N 2 expansion and Casimir scaling of the k-string tensions. Analysis of the closed string channel in this model confirms our conclusions, and provides further insights into the large-N dependence of energy eigenstates and eigenvalues.