diff --git a/requirements/tests.txt b/requirements/tests.txt
index 67b4e08..a5415ea 100644
--- a/requirements/tests.txt
+++ b/requirements/tests.txt
@@ -7,3 +7,4 @@ dj-email-url
 django-cache-url
 # use a unreleased version of invoke since it's compatible with 3.2
 https://github.com/pyinvoke/invoke/archive/771110190ddb729913e8afc67724b84f42e6176d.zip
+six