diff --git a/doc/conf.py b/doc/conf.py
index 9951aed2d..77d2a577a 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -7,6 +7,7 @@ import sphinx
 
 extensions = ['sphinx.ext.autodoc', 'sphinx.ext.doctest', 'sphinx.ext.todo',
               'sphinx.ext.autosummary', 'sphinx.ext.extlinks',
+              'sphinx.ext.intersphinx',
               'sphinx.ext.viewcode', 'sphinx.ext.inheritance_diagram']
 
 master_doc = 'contents'