diff --git a/tox.ini b/tox.ini
index 42e0646..889c383 100644
--- a/tox.ini
+++ b/tox.ini
@@ -27,10 +27,14 @@ commands = flake8 {posargs}
 commands = {posargs}
 
 [testenv:cover]
+# Use python2.7 explicitly so that it's compatible with python2.4 used for plugins.
+basepython=/usr/bin/python2.7
 commands =
   coverage erase
   find . -type f -name "*.pyc" -delete
-  python setup.py testr --coverage --testr-args='{posargs}'
+  coverage run -m unittest discover
+  coverage report
+  coverage html
 
 [testenv:docs]
 commands = python setup.py build_sphinx