diff --git a/download_dataset.py b/download_dataset.py
index fec082b..a744d2c 100644
--- a/download_dataset.py
+++ b/download_dataset.py
@@ -4,9 +4,7 @@
 from tqdm import tqdm
 
 subdir = 'data'
-if not os.path.exists(subdir):
-    os.makedirs(subdir)
-subdir = subdir.replace('\\','/') # needed for Windows
+os.makedirs(subdir, exist_ok=True)
 
 for ds in [
     'webtext',
@@ -18,12 +16,19 @@
     for split in ['train', 'valid', 'test']:
         filename = ds + "." + split + '.jsonl'
         r = requests.get("https://openaipublic.azureedge.net/gpt-2/output-dataset/v1/" + filename, stream=True)
+        r.raise_for_status()
+        file_size = int(r.headers["content-length"])
+        filepath = os.path.join(subdir, filename)
+        try:
+            if os.stat(filepath).st_size == file_size:
+                print('%s already exists and is the expected %d bytes, not redownloading' % (filepath, file_size))
+                r.close()
+                continue
+        except OSError:  # likely "file not found" or similar
+            pass
 
-        with open(os.path.join(subdir, filename), 'wb') as f:
-            file_size = int(r.headers["content-length"])
-            chunk_size = 1000
+        with open(filepath, 'wb') as f:
             with tqdm(ncols=100, desc="Fetching " + filename, total=file_size, unit_scale=True) as pbar:
-                # 1k for chunk_size, since Ethernet packet size is around 1500 bytes
-                for chunk in r.iter_content(chunk_size=chunk_size):
+                for chunk in r.iter_content(chunk_size=4194304):
                     f.write(chunk)
-                    pbar.update(chunk_size)
+                    pbar.update(len(chunk))