diff --git a/trunk/paradiseo-mo/src/perturb/moMonOpPerturb.h b/trunk/paradiseo-mo/src/perturb/moMonOpPerturb.h
index 5a2a7e8e4..c056bbf6a 100644
--- a/trunk/paradiseo-mo/src/perturb/moMonOpPerturb.h
+++ b/trunk/paradiseo-mo/src/perturb/moMonOpPerturb.h
@@ -58,6 +58,7 @@ public:
      */
     bool operator()(EOT& _solution) {
         bool res = monOp(_solution);
+	_solution.invalidate();
         fullEval(_solution);
         return res;
     }