diff --git a/tox.ini b/tox.ini
index 03066fd..5f67cec 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,24 +1,23 @@
 [tox]
-minversion = 1.6
+minversion = 3.1.1
 envlist = docs
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
 install_command = pip install -U {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:pdf-docs]
-basepython = python3
 envdir = {toxworkdir}/docs
 whitelist_externals =
   make