diff --git a/book/_config.yml b/book/_config.yml
index 367f437..a81c825 100644
--- a/book/_config.yml
+++ b/book/_config.yml
@@ -15,6 +15,7 @@ sphinx:
   - sphinx_inline_tabs
   - sphinx.ext.imgconverter
   - teachbooks_favourites
+  - teachbooks_sphinx_grasple
   config:
     html_js_files:
     - https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js