  We derive a QCD sum rule for the inverse moment of the $B_s$-meson light-cone
distribution amplitude in HQET. Within this method, the $SU(3)_{fl}$ symmetry
violation is traced to the strange quark mass and to the difference between
strange and nonstrange quark condensate densities. We predict the ratio of
inverse moments $\lambda_{B_s}/\lambda_B= 1.19 \pm 0.14$ which can be used in
various applications of these distribution amplitudes to the analyses of
$B_{s}$-meson decays, provided an accurate value of $\lambda_B$ is available
from other sources, such as the $B\to \ell \nu_\ell \gamma$ decay.
