diff --git a/incoming/controllers.html b/incoming/controllers.html
index 427f13154e..76acd18955 100644
--- a/incoming/controllers.html
+++ b/incoming/controllers.html
@@ -933,6 +933,12 @@ your <strong>app/Config/Routes.php</strong> file.</p>
 </section>
 <section id="auto-routing-legacy">
 <span id="controller-auto-routing-legacy"></span><h2><a class="toc-backref" href="#id20">Auto Routing (Legacy)</a><a class="headerlink" href="#auto-routing-legacy" title="Permalink to this headline"></a></h2>
+<div class="admonition important">
+<p class="admonition-title">Important</p>
+<p>This feature exists only for backward compatibility. Do not use it
+in new projects. Even if you are already using it, we recommend that you use
+the <a class="reference internal" href="routing.html#auto-routing-improved"><span class="std std-ref">Auto Routing (Improved)</span></a> instead.</p>
+</div>
 <p>This section describes the functionality of Auto Routing (Legacy) that is a routing system from CodeIgniter 3.
 It automatically routes an HTTP request, and executes the corresponding controller method
 without route definitions. The auto-routing is disabled by default.</p>
diff --git a/incoming/routing.html b/incoming/routing.html
index 368a04faa5..31027da4e6 100644
--- a/incoming/routing.html
+++ b/incoming/routing.html
@@ -1463,6 +1463,12 @@ controller <code class="docutils literal notranslate"><span class="pre">Acme\Blo
 </section>
 <section id="auto-routing-legacy">
 <span id="id10"></span><h2><a class="toc-backref" href="#id62">Auto Routing (Legacy)</a><a class="headerlink" href="#auto-routing-legacy" title="Permalink to this headline"></a></h2>
+<div class="admonition important">
+<p class="admonition-title">Important</p>
+<p>This feature exists only for backward compatibility. Do not use it
+in new projects. Even if you are already using it, we recommend that you use
+the <a class="reference internal" href="#auto-routing-improved"><span class="std std-ref">Auto Routing (Improved)</span></a> instead.</p>
+</div>
 <p>Auto Routing (Legacy) is a routing system from CodeIgniter 3.
 It can automatically route HTTP requests based on conventions and execute the corresponding controller methods.</p>
 <p>It is recommended that all routes are defined in the <strong>app/Config/Routes.php</strong> file,