diff --git a/doc/source/conf.py b/doc/source/conf.py
index 29606d9d..a9e98e2b 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -26,7 +26,7 @@ sys.path.append(os.path.join(curpath, '../ext'))
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = ['sphinx.ext.autodoc', 'sphinx.ext.pngmath', 'numpydoc',
-              'sphinx.ext.autosummary']
+              'sphinx.ext.autosummary', 'sphinx.ext.inheritance_diagram']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']