diff --git a/image_geometry/doc/conf.py b/image_geometry/doc/conf.py
index a30006fc0..1cb492d09 100644
--- a/image_geometry/doc/conf.py
+++ b/image_geometry/doc/conf.py
@@ -22,7 +22,7 @@
 
 # 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.doctest', 'sphinx.ext.intersphinx', 'sphinx.ext.pngmath']
+extensions = ['sphinx.ext.autodoc', 'sphinx.ext.doctest', 'sphinx.ext.intersphinx', 'sphinx.ext.imgmath']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']