diff --git a/data/coco.py b/data/coco.py
index 765531761..a1065578a 100644
--- a/data/coco.py
+++ b/data/coco.py
@@ -84,7 +84,11 @@ class COCODetection(data.Dataset):
     """
 
     def __init__(self, root, image_set='trainval35k', transform=None,
-                 target_transform=COCOAnnotationTransform(), dataset_name='MS COCO'):
+                 target_transform=None, dataset_name='MS COCO'):
+
+        if target_transform is None:
+            target_transform = COCOAnnotationTransform()
+
         sys.path.append(osp.join(root, COCO_API))
         from pycocotools.coco import COCO
         self.root = osp.join(root, IMAGES, image_set)
diff --git a/data/voc0712.py b/data/voc0712.py
index a3e80d037..e8718a92b 100644
--- a/data/voc0712.py
+++ b/data/voc0712.py
@@ -96,8 +96,12 @@ class VOCDetection(data.Dataset):
 
     def __init__(self, root,
                  image_sets=[('2007', 'trainval'), ('2012', 'trainval')],
-                 transform=None, target_transform=VOCAnnotationTransform(),
+                 transform=None, target_transform=None,
                  dataset_name='VOC0712'):
+
+        if target_transform is None:
+            target_transform = VOCAnnotationTransform()
+
         self.root = root
         self.image_set = image_sets
         self.transform = transform