  Conventional gauge-fixing schemes such as R$_\xi$ gauges may lead to a
violation of the Higgs-boson low-energy theorem beyond the tree level. To
elucidate this fact, we study a simple model whose U(1) gauge symmetry is
spontaneously broken, and show how the Higgs-boson low-energy theorem can
consistently be extended to the gauge and Higgs sectors of the model. In this
formulation, any gauge-fixing condition must comply with the requirement that
it should be independent of the vacuum expectation value of the Higgs field in
the symmetric limit of the theory. We give a diagrammatic proof of the
Higgs-boson low-energy theorem to all orders in perturbation theory, within the
context of a judiciously modified R$_\xi$ gauge compatible with the above
constraint. The dependence of the kinematic parameters on the Higgs tadpole is
found to be very important for the proof of the theorem.
