diff --git a/4.prioritized dqn.ipynb b/4.prioritized dqn.ipynb
index 04dcfc7..5cc41e5 100644
--- a/4.prioritized dqn.ipynb	
+++ b/4.prioritized dqn.ipynb	
@@ -106,7 +106,7 @@
     "        weights /= weights.max()\n",
     "        weights  = np.array(weights, dtype=np.float32)\n",
     "        \n",
-    "        batch       = zip(*samples)\n",
+    "        batch       = list(zip(*samples))\n",
     "        states      = np.concatenate(batch[0])\n",
     "        actions     = batch[1]\n",
     "        rewards     = batch[2]\n",