diff --git a/docs/documentation/columns/gap.html b/docs/documentation/columns/gap.html
index 6d4b200a..e1378fc3 100644
--- a/docs/documentation/columns/gap.html
+++ b/docs/documentation/columns/gap.html
@@ -194,6 +194,9 @@ doc-subtab: gap
           <code>is-8</code> is the maximum gap of <code>2rem</code>
         </li>
       </ul>
+      <p>
+        Additionally, <code>.is-variable</code> should be added on the <code>.columns</code> container.
+      </p>
     </div>
 
     {% include klmn.html %}