diff --git a/lerobot/common/policies/sac/modeling_sac.py b/lerobot/common/policies/sac/modeling_sac.py
index 43221d5c..3e99dbd4 100644
--- a/lerobot/common/policies/sac/modeling_sac.py
+++ b/lerobot/common/policies/sac/modeling_sac.py
@@ -17,7 +17,6 @@
 
 # TODO: (1) better device management
 
-from copy import deepcopy
 from typing import Callable, Optional, Tuple, Union, Dict, List
 from pathlib import Path
 
@@ -637,9 +636,9 @@ class Policy(nn.Module):
         # Compute standard deviations
         if self.fixed_std is None:
             log_std = self.std_layer(outputs)
-            assert not torch.isnan(log_std).any(), (
-                "[ERROR] log_std became NaN after std_layer!"
-            )
+            assert not torch.isnan(
+                log_std
+            ).any(), "[ERROR] log_std became NaN after std_layer!"
 
             if self.use_tanh_squash:
                 log_std = torch.tanh(log_std)