diff --git a/search-4e.ipynb b/search-4e.ipynb
index c7286c88b..73da69119 100644
--- a/search-4e.ipynb
+++ b/search-4e.ipynb
@@ -825,6 +825,7 @@
     "    def __init__(self, initial, LIFO=False):\n",
     "        \"\"\"Initialize Frontier with an initial Node.\n",
     "        If LIFO is True, pop from the end first; otherwise from front first.\"\"\"\n",
+    "        super(FrontierQ, self).__init__()\n",
     "        self.LIFO = LIFO\n",
     "        self.add(initial)\n",
     "    \n",