diff --git a/src/dynamic_graph/sot/dynamics/humanoid_robot.py b/src/dynamic_graph/sot/dynamics/humanoid_robot.py
index cc56edba05e230b36c7bce2c0fc3860aa62b6b1c..11e816184afcc2d5eb8ca6ae9ae43d6cef187ec6 100755
--- a/src/dynamic_graph/sot/dynamics/humanoid_robot.py
+++ b/src/dynamic_graph/sot/dynamics/humanoid_robot.py
@@ -149,7 +149,7 @@ class AbstractHumanoidRobot (object):
         - one task per operational point to ease robot control
         """
         if not self.dynamic:
-            raise "robots models have to be initialized first"
+            raise RunTimeError("robots models have to be initialized first")
 
         if not self.device:
             self.device = RobotSimu(self.name + '.device')