diff --git a/bindep.txt b/bindep.txt
new file mode 100644
index 0000000..59db2ba
--- /dev/null
+++ b/bindep.txt
@@ -0,0 +1,6 @@
+# This is a cross-platform list tracking distribution packages needed for install and tests;
+# see https://docs.openstack.org/infra/bindep/ for additional information.
+
+# graphviz is necessary for documentation build
+graphviz
+
diff --git a/requirements.txt b/requirements.txt
index 5066bbd..cf5600d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,7 +3,7 @@
 # process, which may cause wedges in the gate later.
 
 pbr!=2.1.0  # Apache-2.0
-sphinx!=1.6.6,!=1.6.7  # BSD
+sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2;python_version>='3.4'  # BSD
 graphviz>=0.4,!=0.5.0  # MIT License
 stestr>=2.0.0
 testtools>=0.9.34
diff --git a/tox.ini b/tox.ini
index de7da91..2b3aa99 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,9 +1,11 @@
 [tox]
-minversion = 2.0
-envlist = docs,py27
+minversion = 3.1.1
+envlist = docs,py37
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
 install_command = pip install -U {opts} {packages}
@@ -11,23 +13,19 @@ deps = -r{toxinidir}/requirements.txt
 commands = stestr run --slowest {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 deps =
     -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
     -r{toxinidir}/requirements.txt
 commands = sphinx-build -W -E -b html -d doc/build/doctrees doc/source doc/build/html
 
 [testenv:doc8]
-basepython = python3
 deps = -r{toxinidir}/requirements.txt doc8
 commands = doc8 doc/source
 
 [testenv:autobuild]
-basepython = python3
 whitelist_externals =
     sphinx-autobuild
 commands =