diff --git a/doc/source/conf.py b/doc/source/conf.py
index 24ec15d..82c939d 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -165,7 +165,6 @@ write_autodoc_index()
 extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.todo',
               'sphinx.ext.coverage',
-              'sphinx.ext.pngmath',
               'sphinx.ext.viewcode',
               'oslosphinx',
               ]