diff --git a/doc/source/conf.py b/doc/source/conf.py
index 374f748e..1fd09e67 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -29,7 +29,7 @@ sys.path.insert(0, os.path.abspath('.'))
 
 # 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.todo', 'sphinx.ext.pngmath']
+extensions = ['sphinx.ext.autodoc', 'sphinx.ext.todo']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']