diff --git a/docs/doc-requirements.txt b/docs/doc-requirements.txt
index ab90481..660b872 100644
--- a/docs/doc-requirements.txt
+++ b/docs/doc-requirements.txt
@@ -1 +1,2 @@
 lxml
+sphinx
diff --git a/tox.ini b/tox.ini
index 245f66e..6a8ef47 100644
--- a/tox.ini
+++ b/tox.ini
@@ -55,8 +55,7 @@ deps =
 basepython = python
 changedir = docs
 deps =
-    lxml
-    sphinx
+    -r{toxinidir}/docs/doc-requirements.txt
 commands =
     sphinx-build [] -W -b html -d {envtmpdir}/doctrees . {envtmpdir}/html