diff --git a/docs/conf.py b/docs/conf.py
index 30b9f2c6aa..cda874ee89 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -55,6 +55,7 @@ def setup(app):
     'sphinx.ext.viewcode',
     'sphinx.ext.githubpages',
     'sphinx.ext.intersphinx',
+    'sphinx_rtd_theme',
     'sphinxcontrib.bibtex',
     'sphinx.ext.napoleon',
     'sphinx_click.ext',