diff --git a/packages/gatsby-plugin-mdx/README.md b/packages/gatsby-plugin-mdx/README.md
index 7b2f7173609fb..fd889fe17ca38 100644
--- a/packages/gatsby-plugin-mdx/README.md
+++ b/packages/gatsby-plugin-mdx/README.md
@@ -405,6 +405,7 @@ module.exports = {
       resolve: `gatsby-plugin-mdx`,
       options: {
         rehypePlugins: [
+          // Generate heading ids for rehype-autolink-headings
           require("rehype-slug"),
           // To pass options, use a 2-element array with the
           // configuration in an object in the second element