diff --git a/Documentation/NuttxPortingGuide.html b/Documentation/NuttxPortingGuide.html
index f68dc3d7963..f24517503ba 100644
--- a/Documentation/NuttxPortingGuide.html
+++ b/Documentation/NuttxPortingGuide.html
@@ -4376,6 +4376,11 @@ build
   <li>
     <code>CONFIG_CAN_NPENDINGRTR</code>: The size of the list of pending RTR requests.  Default: 4
   </li>
+  <li>
+    <code>CONFIG_CAN_LOOPBACK</code>: A CAN driver may or may not support a loopback mode for testing.
+    If the driver does support loopback mode, the setting will enable it.
+    (If the driver does not, this setting will have no effect).
+  </li>
 </ul>
 
 <h3>SPI driver</h3>