The branching fraction for D0 -> K- π+ is measured with the statistics collected by ALEPH from 1991 to 1994. The method is based on the comparison between the rate for the reconstructed D*+ -> D0π+, D0 -> K-π+ decay chain and the rate for inclusive soft pion production at low transverse momentum with respect to the nearest jet. The result is B(D0 -> K- π+) = (3.90 +/- 0.09 +/- 0.12)%
