diff --git a/maskrcnn_benchmark/data/datasets/list_dataset.py b/maskrcnn_benchmark/data/datasets/list_dataset.py
index 70f64c0aa..9058d35b3 100644
--- a/maskrcnn_benchmark/data/datasets/list_dataset.py
+++ b/maskrcnn_benchmark/data/datasets/list_dataset.py
@@ -9,7 +9,7 @@
 
 
 class ListDataset(object):
-    def __init__(self, image_list, transforms=None):
+    def __init__(self, image_lists, transforms=None):
         self.image_lists = image_lists
         self.transforms = transforms
 
@@ -26,7 +26,7 @@ def __getitem__(self, item):
         return img, target
 
     def __len__(self):
-        return len(image_lists)
+        return len(self.image_lists)
 
     def get_img_info(self, item):
         """