  One of the most important O($\alpha_s^2$) corrections to the $B \to X_s
\gamma$ branching ratio originates from interference of contributions from the
current-current and photonic dipole operators. Its value has been estimated
using an interpolation in the charm quark mass between the known results at
$m_c=0$ and for $m_c \ll m_b/2$. An explicit calculation for the physical value
of $m_c$ is necessary to remove the associated uncertainty. In the present
work, we evaluate all the ultraviolet counterterm contributions that are
relevant for this purpose.
