In this paper it is shown that the class of electromagnetic problems for which the operator i(∂/∂t) (where t denotes time) is self-adjoint extends beyond problems involving only insulators and perfect conductors. The class includes problems in which the perfect conductor is generalized to a medium with antisymmetric resistivity tensor. The latter medium approximates media in which helicon waves can propagate. Helicon waves are known to propagate in good conductors in a strong magnetic field B0; it will be found that two necessary conditions for self-adjointness of the operator i(∂/∂t) are that the sample carrying helicons must not have a finite portion parallel to B0, and it must be surrounded by a reflecting surface that prevents energy from escaping.