diff --git a/timm/data/dataset_factory.py b/timm/data/dataset_factory.py
index 194a597e..d0ac30b1 100644
--- a/timm/data/dataset_factory.py
+++ b/timm/data/dataset_factory.py
@@ -26,8 +26,8 @@ _TORCH_BASIC_DS = dict(
     kmnist=KMNIST,
     fashion_mnist=FashionMNIST,
 )
-_TRAIN_SYNONYM = {'train', 'training'}
-_EVAL_SYNONYM = {'val', 'valid', 'validation', 'eval', 'evaluation'}
+_TRAIN_SYNONYM = dict(train=None, training=None)
+_EVAL_SYNONYM = dict(val=None, valid=None, validation=None, eval=None, evaluation=None)
 
 
 def _search_split(root, split):