diff --git a/tianshou/data/batch.py b/tianshou/data/batch.py
index 7e602bba8..f147ca326 100644
--- a/tianshou/data/batch.py
+++ b/tianshou/data/batch.py
@@ -548,6 +548,7 @@ def stack(batches: List[Union[dict, 'Batch']], axis: int = 0) -> 'Batch':
             (2, 4, 5)
 
         .. note::
+
             If there are keys that are not shared across all batches, ``stack``
             with ``axis != 0`` is undefined, and will cause an exception.
         """