1 files changed, 2 insertions, 0 deletions
diff --git a/tox.ini b/tox.ini
index 7892b557a..34bd367d1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -35,6 +35,7 @@ commands =
     python -m flake8 src
 deps =
     flake8>3.0
+    flufl.testing
 
 [testenv:docs]
 basepython = python3
@@ -51,3 +52,4 @@ rc = --rcfile={[coverage]rcfile}
 max-line-length = 79
 exclude = src/mailman/compat/*.py
 jobs = 1
+enable-extensions = U4