diff --git a/docs/source/conf.py b/docs/source/conf.py
index 3bf5b0b1e..38661cdb3 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -44,6 +44,7 @@ extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.mathjax',
               'sphinx.ext.autosummary',
               'sphinx.ext.intersphinx',
+              'sphinx.ext.viewcode',
               'sphinx_numfig',
               'notebook_sphinxext']