diff --git a/doc/requirements.txt b/doc/requirements.txt
new file mode 100644
index 0000000..782c30e
--- /dev/null
+++ b/doc/requirements.txt
@@ -0,0 +1,2 @@
+sphinx>=1.2.3,!=1.6.6,!=1.6.7,<2.0.0;python_version=='2.7'  # BSD
+sphinx!=1.6.6,!=1.6.7,!=2.1.0;python_version>='3.4'  # BSD
diff --git a/requirements.txt b/requirements.txt
index 2abe9b9..64a82ce 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,8 +5,6 @@
 pbr>=0.8
 tortilla>=0.4.1
 Jinja2>=2.7.3
-Sphinx>=1.2.3,<2.0; python_version < '3'
-Sphinx>=1.2.3; python_version >= '3'
 docopt>=0.6.2
 simplejson>=3.8.1
 requests>=2.9.1
diff --git a/tox.ini b/tox.ini
index c73e639..63ab293 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py36,py35,docs
+envlist = py37,py36,py35,py27,docs
 skipsdist = True
 
 [testenv]