diff --git a/tox.ini b/tox.ini
index dd04665..df892dd 100644
--- a/tox.ini
+++ b/tox.ini
@@ -64,9 +64,12 @@ commands =
 
 
 [testenv:docs]
-deps = sphinx
 changedir = docs
-commands=
+deps =
+        sphinx
+        sphinx-book-theme
+
+commands =
         sphinx-build -W -b html . _build/html