diff --git a/18_reinforcement_learning.ipynb b/18_reinforcement_learning.ipynb
index 1e72747..fde8b2b 100644
--- a/18_reinforcement_learning.ipynb
+++ b/18_reinforcement_learning.ipynb
@@ -2511,7 +2511,7 @@
    "source": [
     "import PIL\n",
     "\n",
-    "image_path = os.join(\"images\", \"rl\", \"breakout.gif\")\n",
+    "image_path = os.path.join(\"images\", \"rl\", \"breakout.gif\")\n",
     "frame_images = [PIL.Image.fromarray(frame) for frame in frames[:150]]\n",
     "frame_images[0].save(image_path, format='GIF',\n",
     "                     append_images=frame_images[1:],\n",
@@ -2752,7 +2752,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.6.8"
+   "version": "3.7.4"
   }
  },
  "nbformat": 4,