  We consider compactifications of M-theory on 7-manifolds in the presence of
4-form fluxes, which leave at least four supercharges unbroken. We focus
especially on the case, where the 7-manifold supports two spinors which are
SU(3) singlets and the fluxes appear as specific SU(3) structures. We derive
the constraints on the fluxes imposed by supersymmetry and calculate the
resulting 4-dimensional superpotential.
