  We present a lattice determination of the leptonic decay constant F_Ds of the
Ds-meson using its mass and F_K as experimental input. Setting the scale with
F_K=160 MeV, our final result is F_Ds = 252(9) MeV. The error contains all
uncertainties apart from the quenched approximation. Setting the scale with the
nucleon mass instead leads to an increase of 3(1) MeV of the leptonic decay
constant which might indicate a small quenching error.
