  Let X be a smooth complex manifold. Let Sol denote the solution functor for
D-modules on X. Traditionally, the fully-faithfulness of Riemann-Hilbert
correspondance is proved by showing that if M_1 and M_2 are regular holonomic
D_X modules, then the canonical morphism of complexes of sheaves RH_{M_1,M_2} :
RHom(M_1,M_2) ---> RHom(Sol(M_2),Sol(M_1)) is an isomorphism, in a derived
sense. This paper has to do with the converse statement. We prove that if M is
an holonomic D_X module for which RH_{M,M} is an isomorphism, then M is
regular.
