diff --git a/fetch.bs b/fetch.bs
index 434216456..af711645b 100644
--- a/fetch.bs
+++ b/fetch.bs
@@ -2157,6 +2157,17 @@ Unless stated otherwise, it is false.
 
 <p class=note>This flag is for exclusive use by HTML's render-blocking mechanism. [[!HTML]]
 
+<p>A <a for=/>request</a> has an associated boolean <dfn export for=request>is HTTPS upgrade</dfn>.
+Unless stated otherwise, it is false.
+
+<p class=note>This is for exclusive use by HTTPS Upgrading algorithm.
+
+<p>A <a for=/>request</a> has an associated
+<dfn export for=request>HTTPS upgrade fallback URL</dfn>, which is null or a <a for=/>URL</a>.
+Unless otherwise stated, it is null.
+
+<p class=note>This is for exclusive use by HTTPS Upgrading algorithm.
+
 <hr>
 
 <p>A <a for=/>request</a> has an associated
@@ -3265,6 +3276,106 @@ through TLS using ALPN. The protocol cannot be spoofed through HTTP requests in
 </div>
 
 
+<h3 id=https-upgrades>HTTPS upgrading</h3>
+
+<p>User agents may optionally upgrade requests with URLs that are not
+<a>potentially trustworthy URLs</a> to attempt to fetch them over
+<a>potentially trustworthy URLs</a>. If an upgraded request fails with a network error, it is
+retried over the original URL.
+
+<p>The HTTPS upgrading algorithm consists of <a>upgrade an HTTP request</a> and
+<a>HTTPS upgrade fallback</a> algorithms.
+
+<h4 id=https-upgrades-upgrade>HTTPS upgrade algorithm</h4>
+<div algorithm>
+
+<p>To <dfn>upgrade an HTTP request</dfn> given a <a for=/>request</a> <var>request</var>:
+
+<ol>
+ <li>
+  <p>If one or more of the following conditions are met, return:
+  <ul>
+   <li><p><var>request</var>'s <a for="request">destination</a> is not "<code>document</code>"
+
+   <li><p><var>request</var>'s <a for="request">method</a> is not "<code>GET</code>"
+
+   <li><p><var>request</var>'s <a for="request">URL</a>'s <a for="url">scheme</a> is not
+   "<code>http</code>"
+
+   <li><p><var>request</var>'s <a for="request">URL</a>'s <a for="url">host</a> is exempted from
+   upgrades in an <a>implementation-defined</a> way.
+  </ul>
+ </li>
+
+ <li>
+  <p>If <var>request</var>'s <a for=request>HTTPS upgrade fallback URL</a> is non-null, clear
+  <a for=request>is HTTPS upgrade</a> and <a for=request>HTTPS upgrade fallback URL</a> and return.
+
+  <p class=note>This is a fallback request that shouldn't be upgraded again.
+
+ <li>
+  <p>Otherwise, set the following fields:
+  <ul>
+   <li><p>Set <a for=request>HTTPS upgrade fallback URL</a> to <var>request</var>'s
+   <a for="request">URL</a>.
+
+   <li><p>Set <var>request</var>'s <a for="request">URL</a>'s <a for="url">scheme</a> to
+   "<code>https</code>".
+
+   <li><p>Set <a for=request>is HTTPS upgrade</a> to true.
+  </ul>
+ </li>
+</ol>
+</div>
+
+<h4 id=https-upgrades-fallback>Fallback algorithm</h4>
+<div algorithm>
+
+<p>To run <dfn>HTTPS upgrade fallback</dfn> given a <a for=/>request</a> <var>request</var> and
+<a for=/>response</a> <var>response</var>:
+
+<ol>
+ <li><p>If <var>request</var>'s <a for=request>is HTTPS upgrade</a> is not set, then return
+ <var>response</var>.
+
+ <li>
+  <p>If <var>response</var> is a <a>network error</a>:
+
+  <p class=note>This means that the upgrade failed and initiates a fallback load.
+
+  <ol>
+   <li><p>Let <var>fallbackResponse</var> be a new <a for=/>response</a> whose
+   <a for=response>header list</a> is « », and its <code>Location</code> header is set to
+   <var>request</var>'s <a for=request>HTTPS upgrade fallback URL</a>, and its
+   <a for="response">status</a> set to 307.
+
+   <li><p>Return <var>fallbackResponse</var>.
+  </ol>
+
+ <li>
+  <p>Return <var>response</var>.
+
+  <p class=note>This means the upgrade was successful.
+
+</ol>
+
+<p class=note>User agents can implement a fast-fallback path by canceling slow fetches on upgraded
+requests, in order to quickly initiate a fallback http load.
+
+</div>
+
+<h4 id=http-upgrades-examples>Examples</h4>
+
+<p id=example-https-upgrade-good-https class=example><code>a.com</code> serves both
+<code>http://a.com</code> and <code>https://a.com</code>. An eligible request to
+<code>http://a.com</code> will be upgraded to <code>https://a.com</code>.
+
+<p id=example-https-upgrade-bad-https class=example><code>a.com</code> serves
+<code>http://a.com</code> but refuses connections on <code>https://a.com</code>. An eligible
+request to <code>http://a.com</code> will be upgraded to <code>https://a.com</code>, but the fetch
+will fail. A fallback request will be initiated to <code>http://a.com</code>.
+
+
 
 <h2 id=http-extensions>HTTP extensions</h2>
 
@@ -4445,6 +4556,14 @@ steps:
 
  <li><p><a>Upgrade <var>request</var> to a potentially trustworthy URL, if appropriate</a>.
 
+ <li>
+  <p>Optionally, run <a>upgrade an HTTP request</a> algorithm on <var>request</var>.
+
+  <p class=note>HTTPS upgrading only applies to requests with <a>HTTP(S) scheme</a>s, but it's done
+  in <a>main fetch</a> instead of <a>HTTP fetch</a> to ensure that
+  <a>upgrade a mixed content <var>request</var> to a potentially trustworthy URL, if appropriate</a>
+  step runs next and applies to the upgraded request.
+
  <li><p><a>Upgrade a mixed content <var>request</var> to a potentially trustworthy URL, if appropriate</a>.
 
  <li><p>If <a lt="block bad port">should <var>request</var> be blocked due to a bad port</a>,
@@ -5157,8 +5276,6 @@ these steps:
       <p>If one of the following is true
 
       <ul class=brief>
-       <li><p><var>response</var>'s <a for=response>type</a> is "<code>error</code>"
-
        <li><p><var>request</var>'s <a for=request>mode</a> is "<code>same-origin</code>" and
        <var>response</var>'s <a for=response>type</a> is "<code>cors</code>"
 
@@ -5246,6 +5363,10 @@ these steps:
   <a>CORS check</a>, as <var>request</var>'s <a for=request>client</a> and the service worker can
   have different embedder policies.
 
+ <li><p>If <var>request</var>'s <a for=request>is HTTPS upgrade</a> is set, set <var>response</var>
+ and <var>internalResponse</var> to the result of running <a>HTTPS upgrade fallback</a> given
+ <var>request</var> and <var>response</var>.
+
  <li>
   <p>If <var>internalResponse</var>'s <a for=response>status</a> is a <a>redirect status</a>:
 
@@ -8716,7 +8837,7 @@ resource — for non-<a>CORS requests</a> as well as <a>CORS
 requests</a> — and do not use `<code>Vary</code>`.
 
 
-<h3 class=no-num id=websocket-protocol oldids=websocket-connections,websocket-opening-handshake,fail-the-websocket-connection,the-websocket-connection-is-established>WebSockets</h2>
+<h3 class=no-num id=websocket-protocol oldids=websocket-connections,websocket-opening-handshake,fail-the-websocket-connection,the-websocket-connection-is-established>WebSockets</h3>
 
 <p>As part of establishing a connection, the {{WebSocket}} object initiates a special kind of
 <a for=/>fetch</a> (using a <a for=/>request</a> whose <a for=request>mode</a> is
@@ -8980,6 +9101,7 @@ done only by navigations). The <a>fetch controller</a> is also used to
 <a for=request>redirect mode</a> set to "<code>manual</code>".
 
 
+
 <h2 id=acknowledgments class=no-num>Acknowledgments</h2>
 
 <p>Thanks to