diff --git a/dataset_preprocess.ipynb b/dataset_preprocess.ipynb
index fa7bca1..c15bc31 100644
--- a/dataset_preprocess.ipynb
+++ b/dataset_preprocess.ipynb
@@ -29,6 +29,7 @@
     "import MIDI \n",
     "# Note: The original MIDI.py has poor performance because list.pop(0) has poor performance on some pythons or machines. I changed it to list = list[1:]\n",
     "\n",
+    "import os\n",
     "import glob\n",
     "import re\n",
     "from tqdm import tqdm\n",