diff --git a/doc/conf.py.in b/doc/conf.py.in
index 6dab9d64..34655128 100644
--- a/doc/conf.py.in
+++ b/doc/conf.py.in
@@ -26,7 +26,7 @@ import sphinx_rtd_theme
 
 # 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', 'sphinx.ext.ifconfig']
+extensions = ['sphinx.ext.autodoc', 'sphinx.ext.todo', 'sphinx.ext.imgmath', 'sphinx.ext.ifconfig']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']