diff --git a/icefall/utils.py b/icefall/utils.py
index 3e84fcc6a..09ae6d7c0 100644
--- a/icefall/utils.py
+++ b/icefall/utils.py
@@ -478,8 +478,12 @@ class LossRecord(collections.defaultdict):
         for k, v in zip(keys, s.cpu().tolist()):
             self[k] = v
 
-    def write_summary(self, tb_writer: SummaryWriter, 
-        prefix: str, batch_idx: int) -> None:
+    def write_summary(
+        self,
+        tb_writer: SummaryWriter,
+        prefix: str,
+        batch_idx: int
+    ) -> None:
         """Add logging information to a TensorBoard writer.
         
         Args: