diff --git a/baukit/tokendataset.py b/baukit/tokendataset.py
index c704671..2f6dd34 100644
--- a/baukit/tokendataset.py
+++ b/baukit/tokendataset.py
@@ -50,11 +50,13 @@ def move_to(device, *containers):
                 g = enumerate(container)
             for i, v in g:
                 moved = move_to(device, v)
-                if moved is not None:
+                if moved is not None and moved is not v:
                     container[i] = moved
         elif isinstance(container, (torch.nn.Parameter, torch.Tensor)):
             assert len(containers) == 1, 'Use move_to to move tensors in containers.'
             return container.to(device)
+    if len(containers) == 1:
+        return container
 
 
 def length_collation(token_size):