diff --git a/tox.ini b/tox.ini
index 006dbffe3ec5..b87dcef0610a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -155,6 +155,7 @@ deps =
     {[testing]deps}
     pycodestyle
     pylint >= 1.6.4
+    sphinx
 setenv =
     PYTHONPATH = {toxinidir}/_testing
 passenv = {[testenv:system-tests]passenv}