Manipulation of a mechanism by the principal himself is an issue in a context where there is no grand-mechanism linking the principal and his agents who are instead tied together by a set of bilateral contracts. Taking into account the possibility of manipulations and focusing on mechanisms which are robust to such manipulations restores continuity of the optimal mechanism with respect to the information structure and goes in the direction of modelling weaker institutions than currently assumed in the mechanism design literature. The authors present an overview of our ongoing research on the subject and highlight some promising applications. (A paraître dans : Economie Publique).