  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.

High Energy Physics - Phenomenology