diff --git a/docs/source/conf.py b/docs/source/conf.py
index 84175cb43..4f5fffb67 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -18,7 +18,7 @@
 def setup(app):
     app.add_css_file("main_stylesheet.css")
 
-extensions = ['breathe']
+extensions = ['breathe', 'sphinx_rtd_theme']
 breathe_projects = { 'xtensor': '../xml' }
 breathe_default_project = "xtensor"
 templates_path = ['_templates']