diff --git a/download_data.py b/download_data.py
index 3d8d5d1..27fedf9 100644
--- a/download_data.py
+++ b/download_data.py
@@ -216,7 +216,8 @@ def download_data(dataset,
 
     parser.add_argument(
         "--split",
-        choices=["Training", "Validation"],
+        choices=[None, "Training", "Validation"],
+        default=None
     )
 
     parser.add_argument(