diff --git a/docs/extensions/pymdown.md b/docs/extensions/pymdown.md
index e82a8e891..eba1970e4 100644
--- a/docs/extensions/pymdown.md
+++ b/docs/extensions/pymdown.md
@@ -182,13 +182,13 @@ runtime needs to be included. This can be done with
 [additional JavaScript][20]:
 
 ``` yaml
-extra_js:
+extra_javascript:
   - 'https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-MML-AM_CHTML'
 ```
 
 If you want to override the default MathJax configuration, you can do this by
-adding another JavaScript file **before** the MathJax runtime in `extra_js`
-which contains your MathJax configuration, e.g.:
+adding another JavaScript file **before** the MathJax runtime in
+`extra_javascript` which contains your MathJax configuration, e.g.:
 
 ``` js
 MathJax.Hub.Config({		
@@ -213,6 +213,14 @@ MathJax.Hub.Config({
 });
 ```
 
+In your `mkdocs.yml`, include it with:
+
+``` yaml
+extra_javascript:
+  - 'extra.js'
+  - 'https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-MML-AM_CHTML'
+```
+
   [17]: https://facelessuser.github.io/pymdown-extensions/extensions/arithmatex/
   [18]: https://www.mathjax.org/
   [19]: http://meta.math.stackexchange.com/questions/5020/