  We calculate the radiative corrections to the nonleptonic inclusive B decay
mode $b\to c ud$ taking into account the charm quark mass. The corrections
increase the decay rate by (4--8)\%, depending on the renormalization point.
Using these results, we obtain an improved theoretical prediction for the
semileptonic branching ratio of B mesons. This talk relies on work done in
collaboration with E. Bagan, V.M.\ Braun and P. Gosdzinsky.
