diff --git a/examples/pybullet/gym/pybullet_envs/bullet/cartpole_bullet.py b/examples/pybullet/gym/pybullet_envs/bullet/cartpole_bullet.py
index d0f833a2a..399b7f455 100644
--- a/examples/pybullet/gym/pybullet_envs/bullet/cartpole_bullet.py
+++ b/examples/pybullet/gym/pybullet_envs/bullet/cartpole_bullet.py
@@ -1,6 +1,6 @@
 """
 Classic cart-pole system implemented by Rich Sutton et al.
-Copied from https://webdocs.cs.ualberta.ca/~sutton/book/code/pole.c
+Copied from http://incompleteideas.net/book/code/pole.c
 """
 import os, inspect
 currentdir = os.path.dirname(os.path.abspath(inspect.getfile(inspect.currentframe())))