diff --git a/utils/collate.py b/utils/collate.py
index a3f6ad0e..55a9db13 100755
--- a/utils/collate.py
+++ b/utils/collate.py
@@ -5,7 +5,7 @@
 import torch
 import numpy as np
 import collections
-from torch._six import string_classes
+string_classes = str
 
 
 """ Custom collate function """