diff --git a/doc/source/conf.py b/doc/source/conf.py
index 1d7e84b2..fd508716 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -38,7 +38,7 @@ sys.path.append(os.path.abspath('../bin'))
 # 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.todo',
-              'sphinx.ext.coverage', 'sphinx.ext.pngmath',
+              'sphinx.ext.coverage',
               'sphinx.ext.viewcode', 'ext.cli']
 
 if not on_rtd: