diff --git a/src/engine.py b/src/engine.py
index 565a35e..e7d75d5 100644
--- a/src/engine.py
+++ b/src/engine.py
@@ -7,10 +7,14 @@
 import torch.nn as nn
 import torch.nn.functional as F
 from torch.utils.data import DataLoader
-from tqdm import tqdm
 
 
 def train_one_epoch(model, loader: DataLoader, opt, loss_fn=None) -> float:
+    """Standard training epoch. tqdm is imported lazily so that callers that
+    only need `distillation_loss` or `benchmark_latency` (e.g. the unit-test
+    path) do not pay the tqdm install cost."""
+    from tqdm import tqdm  # noqa: PLC0415
+
     model.train()
     if loss_fn is None:
         loss_fn = nn.CrossEntropyLoss()