diff --git a/docs/conf.py b/docs/conf.py
index 1af5148..a6f3367 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -38,6 +38,7 @@ autodoc_member_order = 'bysource'
 extensions = [
     'sphinx.ext.autodoc',
     'sphinx.ext.viewcode',
+    'sphinx_rtd_theme',
 ]
 
 # Add any paths that contain templates here, relative to this directory.