diff --git a/src/problem-solver.cc b/src/problem-solver.cc
index 8ea60146502371b05b7dd29679c7f94edb5dc1f6..7ad6ff534eefc99d5a4c6557cf39ba65c4bb47dc 100644
--- a/src/problem-solver.cc
+++ b/src/problem-solver.cc
@@ -30,6 +30,11 @@
 
 namespace hpp {
   namespace manipulation {
+    std::ostream& operator<< (std::ostream& os, const Robot& robot)
+    {
+      return robot.print (os);
+    }
+
     void ProblemSolver::buildCompositeRobot (const std::string& robotName,
 					     const Names_t& robotNames)
     {