diff --git a/tox.ini b/tox.ini
index a7593871..81c851e1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,8 +9,11 @@ deps=
 passenv=HTTP_PROXY HTTPS_PROXY http_proxy https_proxy NO_PROXY no_proxy
 setenv=
     VIRTUAL_ENV={envdir}
+basepython = python3.5
 usedevelop = True
 install_command = pip install {opts} {packages}
+whitelist_externals = find
+                      flake8
 commands =
   find . -type f -name "*.pyc" -delete
   python -V
@@ -38,7 +41,7 @@ commands =
 
 [testenv:coverage]
 commands =
-  pytest \
+  python -m pytest \
     --cov-branch \
     --cov-report term-missing:skip-covered \
     --cov-config .coveragerc \