diff --git a/tox.ini b/tox.ini
index 0d72ecc4..aacf1807 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,7 +9,9 @@ usedevelop = True
 install_command = pip install -U {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+commands = find . -type f -name "*.pyc" -delete
+           python setup.py testr --slowest --testr-args='{posargs}'
+whitelist_externals = find
 
 [testenv:pypy]
 deps = setuptools<3.2