diff --git a/ml5/2_6_1_Q-Learning.ipynb b/ml5/2_6_1_Q-Learning.ipynb
index 84cabb1..601b961 100644
--- a/ml5/2_6_1_Q-Learning.ipynb
+++ b/ml5/2_6_1_Q-Learning.ipynb
@@ -61,7 +61,13 @@
     "foo@bar:~$ pip install gym\n",
     "```\n",
     "\n",
-    "If you want to try the Atari environment, it is better that you opt for the full installation from the source. Follow the instructions at [https://github.com/openai/gym#id15](OpenGym)."
+    "\n",
+    "If you get the error message 'NotImplementedError: abstract', [execute](https://github.com/openai/gym/issues/775) \n",
+    "```console\n",
+    "foo@bar:~$ pip install pyglet==1.2.4\n",
+    "```\n",
+    "\n",
+    "If you want to try the Atari environment, it is better that you opt for the full installation from the source. Follow the instructions at [https://github.com/openai/gym#id15](OpenGym).\n"
    ]
   },
   {