diff --git a/python/mjspec.ipynb b/python/mjspec.ipynb
index b933fac3..ff4b997e 100644
--- a/python/mjspec.ipynb
+++ b/python/mjspec.ipynb
@@ -97,6 +97,7 @@
     "\n",
     "# Other imports and helper functions\n",
     "import numpy as np\n",
+    "import random\n",
     "from scipy.signal import convolve2d\n",
     "\n",
     "# Graphics and plotting.\n",