  The charged-Higgs contributions to the decay \bar{B} -> X_s gamma are
discussed in the minimal supersymmetric standard model at large tan beta. These
contributions receive two-loop O(alpha_s tan beta) corrections by squark-gluino
subloops, which are nondecoupling in the limit of heavy superpartners and
possibly large. Their leading parts are already known and were evaluated by
using an effective two-Higgs-doublet Lagrangian. Subleading corrections coming
from higher-dimension operators in the effective Lagrangian were ignored,
although this is not, a priori, justified when m_{H^\pm} is not much smaller
than the typical supersymmetric mass M_{SUSY}. Here, we calculate all
subleading terms of the O(alpha_s tan beta) corrections up to
O((m_t^2,m_{H^\pm}^2/M_{SUSY}^2)^2), as well as all the exact two-loop diagrams
with squark-gluino subloops, beyond the effective-Lagrangian approximation.
Comments are made on the size of these corrections.
