diff --git a/flair/trainers/trainer.py b/flair/trainers/trainer.py
index 826083797b..543576c197 100644
--- a/flair/trainers/trainer.py
+++ b/flair/trainers/trainer.py
@@ -612,7 +612,9 @@ def train_custom(
                         train_loss = batch_train_loss / batch_train_samples
                         self._record(MetricRecord.scalar(("train", "batch_loss"), train_loss, total_train_samples))
                         if gradient_norm is not None:
-                            self._record(MetricRecord.scalar(("train", "gradient_norm"), gradient_norm, total_train_samples))
+                            self._record(
+                                MetricRecord.scalar(("train", "gradient_norm"), gradient_norm, total_train_samples)
+                            )
 
                         epoch_train_loss += batch_train_loss
                         epoch_train_samples += batch_train_samples