diff --git a/protocol.html b/protocol.html
index 546bae54..336788dd 100644
--- a/protocol.html
+++ b/protocol.html
@@ -688,6 +688,40 @@ <h2 property="schema:name">Notifications</h2>
               <p>A Solid server MUST conform to the LDN specification by implementing the Receiver parts to receive notifications and make Inbox contents available [<cite><a class="bibref" href="#bib-ldn">LDN</a></cite>].</p>
 
               <p>A Solid client MUST conform to the LDN specification by implementing the Sender or Consumer parts to discover the location of a resource’s Inbox, and to send notifications to an Inbox or to retrieve the contents of an Inbox [<cite><a class="bibref" href="#bib-ldn">LDN</a></cite>].</p>
+
+              <section id="inbox-discovery-client-error" inlist="" rel="schema:hasPart" resource="#inbox-discovery-client-error">
+                <h3 property="schema:name">Inbox Discovery on Client Error</h3>
+                <div datatype="rdf:HTML" property="schema:description">
+                  <p>This section extends the LDN protocol to allow the discovery of the Inbox URL of a target resource on client errors (HTTP responses with <code>4xx</code> status codes) [<cite><a class="bibref" href="#bib-rfc7231">RFC7231</a></cite>][<cite><a class="bibref" href="#bib-ldn">LDN</a></cite>].</p>
+
+                  <p>Servers who want to advertise the Inbox URL in an HTTP response with a <code>4xx</code> status code, <code>MUST</code> do only one of the following:</p>
+
+                  <ul>
+                    <li>Include the <code>Link</code> header with a <code>rel</code> value of <code>http://www.w3.org/ns/ldp#inbox</code>.</li>
+                    <li>Return an RDF representation [<cite><a class="bibref" href="#bib-rdf11-concepts">RDF11-CONCEPTS</a></cite>], whose encoded RDF graph contains a relation of type <code>http://www.w3.org/ns/ldp#inbox</code>. The subject of that relation is the target resource and the object is the Inbox.</li>
+                  </ul>
+
+                  <p>Senders do the following to discover the Inbox URL in an HTTP response with a <code>4xx</code> status code:</p>
+
+                  <ul>
+                    <li>Use the <code>Link</code> header with a <code>rel</code> value of <code>http://www.w3.org/ns/ldp#inbox</code>.</li>
+                    <li>Parse an RDF representation [<cite><a class="bibref" href="#bib-rdf11-concepts">RDF11-CONCEPTS</a></cite>], whose encoded RDF graph contains a relation of type <code>http://www.w3.org/ns/ldp#inbox</code>. The subject of that relation is the target resource and the object is the Inbox.</li>
+                  </ul>
+
+                  <p>These may be carried out in either order, but if the first fails to result in an Inbox the second MUST be tried.</p>
+
+                  <figure class="listing example" id="discovery-put-example-403" rel="schema:hasPart" resource="#discovery-turtle-example-webid">
+                    <p class="example-h">Discovery example: Client error</p>
+                    <pre about="#discovery-put-example-403" property="schema:description" typeof="fabio:Script"><code>PUT /article HTTP/1.1</code>
+<code>Host: example.org</code>
+<code>Content-Type: text/html;charset=utf-8</code>
+<code></code>
+<code>HTTP/1.1 403 Forbidden</code>
+<code>Link: &lt;http://example.org/inbox/&gt; rel="http://www.w3.org/ns/ldp#inbox"</code></pre>
+                    <figcaption>Discovering an Inbox in the response of a rejected request.</figcaption>
+                  </figure>
+                </div>
+              </section>
             </div>
           </section>