diff --git a/site/_docs/themes.md b/site/_docs/themes.md
index 2b7155bb..02e1ebf5 100644
--- a/site/_docs/themes.md
+++ b/site/_docs/themes.md
@@ -4,6 +4,15 @@ title: Themes
 permalink: /docs/themes/
 ---
 
+<div class="note unreleased">
+  <h5>This feature is unreleased!</h5>
+  <p>
+    Jekyll 3.0 and 3.1 do NOT have the ability to add themes in this way.
+    The documentation below is for an unreleased version of Jekyll and
+    cannot be used at the moment.
+  </p>
+</div>
+
 Jekyll has an extensive theme system, which allows you to leverage community-maintained templates and styles to customize your site's presentation. Jekyll themes package layouts, includes, and stylesheets in a way that can be overridden by your site's content.
 
 ## Installing a theme