  Observing a heavy charged Higgs boson produced in the near future at the
Tevatron or at the LHC would be instant evidence of physics beyond the Standard
Model. Whether such a Higgs boson would be supersymmetric or not it could only
be decided after accurate prediction of its properties. Here we compute the
decay width of the dominant decay of such a boson, namely H^+ -> t \bar{b},
including the leading electroweak corrections originating from large Yukawa
couplings within the MSSM. These electroweak effects turn out to be of
comparable size to the O(alpha_s) QCD corrections in relevant portions of the
MSSM parameter space. Our analysis incorporates the stringent low-energy
constraints imposed by radiative B-meson decays.
