diff --git a/tox.ini b/tox.ini
index fe925951b..208aaa4aa 100644
--- a/tox.ini
+++ b/tox.ini
@@ -58,6 +58,7 @@ deps =
     -ctests/constraints.txt
     -rrequirements-py3.txt
     -rtests/requirements-py3.txt
+    mock
     # Extras
     botocore>=1.3.23
     Pillow>=3.4.2