diff --git a/tox.ini b/tox.ini
index 63994ca..3e2877f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -10,7 +10,11 @@ setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+whitelist_externals = find
+commands =
+    find . -type f -name "*.py[c|o]" -delete
+    find . -type d -name "__pycache__" -delete
+    python setup.py testr --slowest --testr-args='{posargs}'
 
 [testenv:pypy]
 deps = setuptools<3.2