diff --git a/static/build.html b/static/build.html
index 57e2190d..0ec4acb3 100644
--- a/static/build.html
+++ b/static/build.html
@@ -261,6 +261,9 @@
                 <li>zip</li>
             </ul>
 
+            <p>The <code>signify</code> tool (with the proper naming) is also required for signing
+            factory images zips.</p>
+
             <h2 id="downloading-source-code">
                 <a href="#downloading-source-code">Downloading source code</a>
             </h2>