diff --git a/pyrobolearn/worlds/world.py b/pyrobolearn/worlds/world.py
index 3d30874..5b9c4f0 100644
--- a/pyrobolearn/worlds/world.py
+++ b/pyrobolearn/worlds/world.py
@@ -390,7 +390,7 @@ class World(object):
         #     bridge.step()
 
         # call the step method for each body
-        for body in self.bodies:
+        for body in self.bodies.values():
             body.step()
 
         # call simulation step