diff --git a/rankers/train/loss/__init__.py b/rankers/train/loss/__init__.py
index 171928b..df34cec 100644
--- a/rankers/train/loss/__init__.py
+++ b/rankers/train/loss/__init__.py
@@ -1,3 +1,4 @@
+from abc import abstractmethod
 import torch.nn as nn
 import torch
 from torch import Tensor