diff --git a/18_reinforcement_learning.ipynb b/18_reinforcement_learning.ipynb
index fe276a1..10e07b6 100644
--- a/18_reinforcement_learning.ipynb
+++ b/18_reinforcement_learning.ipynb
@@ -57,7 +57,7 @@
     "    # %tensorflow_version only exists in Colab.\n",
     "    %tensorflow_version 2.x\n",
     "    !apt update && apt install -y libpq-dev libsdl2-dev swig xorg-dev xvfb\n",
-    "    !pip install -q -U tf-agents pyvirtualdisplay gym[atari]\n",
+    "    !pip install -q -U tf-agents pyvirtualdisplay gym[atari,box2d]\n",
     "    IS_COLAB = True\n",
     "except Exception:\n",
     "    IS_COLAB = False\n",