diff --git a/eo/src/moo/eoNSGA_II_Eval.h b/eo/src/moo/eoNSGA_II_Eval.h
index c3db1970..68a4cb2f 100644
--- a/eo/src/moo/eoNSGA_II_Eval.h
+++ b/eo/src/moo/eoNSGA_II_Eval.h
@@ -19,7 +19,7 @@ class eoNSGA_II_Eval : public eoMOEval<EOT>
   eoNSGA_II_Eval(eoEvalFunc<EOT>& eval)    : eoMOEval<EOT>(eval) {}
   eoNSGA_II_Eval(eoPopEvalFunc<EOT>& eval) : eoMOEval<EOT>(eval) {}
     
-    void operator()(eoPop<EOT>& parents, eoPop<EOT>& offspring) {
+    virtual void operator()(eoPop<EOT>& parents, eoPop<EOT>& offspring) {
         eval(parents, offspring);
 
         std::vector<EOT*> pop;
diff --git a/eo/src/moo/eoNSGA_IIa_Eval.h b/eo/src/moo/eoNSGA_IIa_Eval.h
index f7e71b37..c9131871 100644
--- a/eo/src/moo/eoNSGA_IIa_Eval.h
+++ b/eo/src/moo/eoNSGA_IIa_Eval.h
@@ -18,7 +18,7 @@ class eoNSGA_IIa_Eval : public eoMOEval<EOT>
   eoNSGA_IIa_Eval(eoPopEvalFunc<EOT>& eval) : eoMOEval<EOT>(eval) {}
   
 
-  void operator()(eoPop<EOT>& parents, eoPop<EOT>& offspring) {
+  virtual void operator()(eoPop<EOT>& parents, eoPop<EOT>& offspring) {
         eval(parents, offspring);
 
         std::vector<EOT*> pop;
diff --git a/eo/src/moo/eoNSGA_I_Eval.h b/eo/src/moo/eoNSGA_I_Eval.h
index 27733bd7..56824dcf 100644
--- a/eo/src/moo/eoNSGA_I_Eval.h
+++ b/eo/src/moo/eoNSGA_I_Eval.h
@@ -14,7 +14,7 @@ public :
   eoNSGA_I_Eval(double nicheWidth, eoEvalFunc<EOT>& eval)    : eoMOEval<EOT>(eval), nicheSize(nicheWidth) {}
   eoNSGA_I_Eval(double nicheWidth, eoPopEvalFunc<EOT>& eval) : eoMOEval<EOT>(eval), nicheSize(nicheWidth) {}
 
-  void operator()(eoPop<EOT>& parents, eoPop<EOT>& offspring) {
+  virutal void operator()(eoPop<EOT>& parents, eoPop<EOT>& offspring) {
         eval(parents, offspring);
 
         std::vector<EOT*> pop;