diff --git a/doc/source/conf.py b/doc/source/conf.py
index 6683c4579..03eaf79de 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -31,7 +31,6 @@ sys.path.insert(0, os.path.abspath('./'))
 
 extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.coverage',
-              'sphinx.ext.pngmath',
               'sphinx.ext.ifconfig',
               'sphinx.ext.graphviz',
               'oslosphinx',