diff --git a/tox.ini b/tox.ini
index 4e7b543a..0a51741a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -54,9 +54,9 @@ commands =
 [testenv:docs]
 deps =
     sphinx
-    sphinx_rtd_theme
+    sphinx-rtd-theme==1.1.1
     sphinx-notfound-page
-    sphinx_copybutton
+    sphinx-copybutton
     restructuredtext-lint
 commands =
     sphinx-build -W -b html -d {envtmpdir}/doctrees docs docs/_build/html
@@ -64,6 +64,6 @@ commands =
 [testenv:docslinkcheck]
 deps =
     sphinx
-    sphinx_rtd_theme
+    sphinx-rtd-theme
 commands =
     sphinx-build -W -b linkcheck docs docs/_build/html