diff --git a/docs/configuration.md b/docs/configuration.md
index 9650b6e49fb1de054a80fae02fa013ced7a18614..c557b0d19561a21ff5bed6d82f39dd0527af8c19 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -111,7 +111,7 @@ location with this method.
 </tr>
 <tr>
   <td>`extends`</td>
-  <td>Configuration presets to use/extend</td>
+  <td>Configuration presets to use/extend. Note: does not work if configured in config.js</td>
   <td>list</td>
   <td><pre>[]</pre></td>
   <td>`RENOVATE_EXTENDS`</td>
diff --git a/lib/config/definitions.js b/lib/config/definitions.js
index fb9cb445137a10c91dbdc81055c8967197c419de..44be7fcbf6c29c4bd453701257c427d915f61ea2 100644
--- a/lib/config/definitions.js
+++ b/lib/config/definitions.js
@@ -19,7 +19,8 @@ module.exports = {
 const options = [
   {
     name: 'extends',
-    description: 'Configuration presets to use/extend',
+    description:
+      'Configuration presets to use/extend. Note: does not work if configured in config.js',
     stage: 'package',
     type: 'list',
     allowString: true,