diff --git a/packages/gatsby-plugin-mdx/gatsby-node.js b/packages/gatsby-plugin-mdx/gatsby-node.js
index 4d2099a4eb55a..3cd212028f614 100644
--- a/packages/gatsby-plugin-mdx/gatsby-node.js
+++ b/packages/gatsby-plugin-mdx/gatsby-node.js
@@ -124,6 +124,6 @@ exports.pluginOptionsSchema = function ({ Joi }) {
       ),
     root: Joi.string()
       .default(process.cwd())
-      .description(`Who knows what this does lol`)
+      .description(`[deprecated] This is a legacy option that used to define root directory of the project. It was needed to generate a cache directory location. It currently has no effect.`)
   })
 }