diff --git a/doc/_templates/layout.html b/doc/_templates/layout.html
index 974009cc5..58fe13fa7 100644
--- a/doc/_templates/layout.html
+++ b/doc/_templates/layout.html
@@ -1,4 +1,15 @@
 {% extends "!layout.html" %}
+{% block document %}
+  {% if not is_release %}
+    <div class="admonition important">
+        <p class="admonition-title">Important</p>
+        <p>This is the latest documentation for the unstable development branch of
+        Project ACRN (master).<br/>Use the drop-down menu on the left to select
+        documentation for a stable release such as <a href="/2.7/">v2.7</a>.</p>
+    </div>
+  {% endif %}
+  {{ super() }}
+{% endblock %}
 {% block menu %}
   {% include "aversions.html" %}
   {{ super() }}