diff --git a/tinystories.py b/tinystories.py
index 9a69cb8..419e0d5 100644
--- a/tinystories.py
+++ b/tinystories.py
@@ -8,7 +8,7 @@ import json
 import os
 import random
 from typing import List
-from concurrent.futures import ThreadPoolExecutor, as_completed
+from concurrent.futures import ProcessPoolExecutor
 
 import numpy as np
 import requests
@@ -66,34 +66,35 @@ def download():
     print(f"Number of shards: {len(shard_filenames)}")
     print(f"Example story:\n{data[0]}")
 
-def pretokenize():
+
+def process_shard(args):
+    shard_id, shard = args
     enc = Tokenizer()
+    with open(shard, "r") as f:
+        data = json.load(f)
+    all_tokens = []
+    for example in tqdm(data, position=shard_id):
+        text = example["story"]
+        text = text.strip()  # get rid of leading/trailing whitespace
+        tokens = enc.encode(text, bos=True, eos=False)  # encode the text, use BOS
+        all_tokens.extend(tokens)
+    # convert to uint16 nparray
+    all_tokens = np.array(all_tokens, dtype=np.uint16)
+    # write to disk
+    tokenized_filename = shard.replace(".json", ".bin")
+    with open(tokenized_filename, "wb") as f:
+        f.write(all_tokens.tobytes())
+    print(f"Saved {tokenized_filename}")
 
-    def process_shard(shard):
-        with open(shard, "r") as f:
-            data = json.load(f)
-        all_tokens = []
-        for example in tqdm(data):
-            text = example["story"]
-            text = text.strip() # get rid of leading/trailing whitespace
-            tokens = enc.encode(text, bos=True, eos=False)  # encode the text, use BOS
-            all_tokens.extend(tokens)
-        # convert to uint16 nparray
-        all_tokens = np.array(all_tokens, dtype=np.uint16)
-        # write to disk
-        tokenized_filename = shard.replace(".json", ".bin")
-        with open(tokenized_filename, "wb") as f:
-            f.write(all_tokens.tobytes())
-        print(f"Saved {tokenized_filename}")
 
+def pretokenize():
     # iterate the shards and tokenize all of them one by one
     data_dir = os.path.join(DATA_CACHE_DIR, "TinyStories_all_data")
     shard_filenames = sorted(glob.glob(os.path.join(data_dir, "*.json")))
 
-    # process all the shards in a threadpool
-    with ThreadPoolExecutor(max_workers=8) as executor:
-        executor.map(process_shard, shard_filenames)
-
+    # process all the shards in a process pool
+    with ProcessPoolExecutor() as executor:
+        executor.map(process_shard, enumerate(shard_filenames))
     print("Done.")
 
 
@@ -163,4 +164,5 @@ if __name__ == "__main__":
         "download": download,
         "pretokenize": pretokenize,
     }
-    fun[args.stage]()
\ No newline at end of file
+    fun[args.stage]()
+