diff --git a/icefall/utils.py b/icefall/utils.py
index 09ae6d7c0..cfb6b686e 100644
--- a/icefall/utils.py
+++ b/icefall/utils.py
@@ -482,14 +482,14 @@ class LossRecord(collections.defaultdict):
         self,
         tb_writer: SummaryWriter,
         prefix: str,
-        batch_idx: int
+        batch_idx: int,
     ) -> None:
         """Add logging information to a TensorBoard writer.
-        
+
         Args:
             tb_writer: a TensorBoard writer
-            prefix: a prefix for the name of the loss, 
-                    e.g. "train/valid_", or "train/current_".
+            prefix: a prefix for the name of the loss, e.g. "train/valid_",
+                or "train/current_"
             batch_idx: The current batch index, used as the x-axis of the plot.
         """
         for k, v in self.norm_items():