diff --git a/tests/test_sanitize.py b/tests/test_sanitize.py
index f9d8db54..ab1a66f2 100644
--- a/tests/test_sanitize.py
+++ b/tests/test_sanitize.py
@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-from io import StringIO
+from six import StringIO
 import numpy as np
 import pandas as pd
 import cooler