diff --git a/doc/source/conf.py b/doc/source/conf.py
index 9a905b8009..04653f3049 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -74,7 +74,6 @@ extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.viewcode',
               'sphinx.ext.todo',
               'sphinx.ext.coverage',
-              'sphinx.ext.pngmath',
               'sphinx.ext.viewcode',
               'sphinx.ext.doctest',
               'oslosphinx',