  We obtain the vacuum solutions for M-theory compactified on eight-manifolds
with non-vanishing four-form flux by analyzing the scalar potential appearing
in the three-dimensional theory. Many of these vacua are not supersymmetric and
yet have a vanishing three-dimensional cosmological constant. We show that in
the context of Type IIB compactifications on Calabi-Yau threefolds with fluxes
and external brane sources alpha'-corrections generate a correction to the
supergravity potential proportional to the Euler number of the internal
manifold which spoils the no-scale structure appearing in the classical
potential. This indicates that alpha'-corrections may indeed lead to a
stabilization of the radial modulus appearing in these compactifications.
