diff --git a/doc/user-manual/conf.py b/doc/user-manual/conf.py
index 899f5d6..9475d85 100644
--- a/doc/user-manual/conf.py
+++ b/doc/user-manual/conf.py
@@ -25,7 +25,7 @@ import sys, os
 
 # 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.intersphinx', 'sphinx.ext.pngmath']
+extensions = ['sphinx.ext.intersphinx', 'sphinx.ext.imgmath']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']