diff --git a/tox.ini b/tox.ini
index 2e8d9ee0f..6a01501fb 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,6 +6,7 @@ envlist = py{27,37}-cov, htmlcov
 deps =
     cov: coverage>=4.3
     pytest
+    pytest-randomly
     -rrequirements.txt
 extras =
     ufo