  We compute next-to-leading order QCD corrections to the CP asymmetry a_{fs} =
Im(Gamma_{12}/M_{12}) in flavour-specific B_{d,s} decays such as B_d->X l nu or
B_s->D^-_s pi^+. The corrections reduce the uncertainties associated with the
choice of the renormalization scheme for the quark masses significantly. In the
Standard Model we predict a^d_{fs} = -(5.0 +- 1.1)*10^{-4}. As a by-product we
also obtain the width difference in the B_d system at next-to-leading order in
QCD.
