  We show that the inclusion of a term $C_{abcd}C^{abcd}$ in the action can
remove the recently described anisotropic singularity occurring on the
hypersurface $F(\phi)=0$ of scalar-tensor theories of gravity of the type $$
S=\int d^4x \sqrt{-g} {F(\phi)R - \partial_a\phi\partial^a\phi -2V(\phi)}, $$
preserving, by construction, all of their isotropic solutions. We show that, in
principle, a higher order term of this type can arise from considerations about
the renormalizability of the semiclassical approach to the theory. Such result
brings again into consideration the quintessential models recently proposed
based in a conformally coupled scalar field ($F(\phi)=1-{1/6}\phi^2$) with
potential $V(\phi)=\frac{m}{2}\phi^2 -\frac{\Omega}{4}\phi^4$, that have been
discharged as unrealistic precisely by their anisotropic instabilities on the
hypersurface $F(\phi)=0$.
