diff --git a/fetch.bs b/fetch.bs
index f00f3c966..9ff99624f 100755
--- a/fetch.bs
+++ b/fetch.bs
@@ -1420,6 +1420,21 @@ downloads. This format of range header value can be set using <a>add a range hea
 have this value start with `<code>Mozilla/5.0 (</code>` and be generally modeled after other web
 browsers.
 
+<div algorithm>
+<p>To get the <a>environment settings object</a> <var>environment</var>'s
+<dfn export>environment default `<code>User-Agent</code>` value</dfn>:
+
+<ol>
+ <li><p>Let <var>userAgent</var> be the <a>WebDriver BiDi emulated User-Agent</a> for
+ <var>environment</var>.
+
+ <li><p>If <var>userAgent</var> is non-null, then return <var>userAgent</var>,
+ <a>isomorphic encoded</a>.
+
+ <li><p>Return the <a>default `<code>User-Agent</code>` value</a>.
+</ol>
+</div>
+
 <p>The <dfn>document `<code>Accept</code>` header value</dfn> is
 `<code>text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8</code>`.
 
@@ -5986,11 +6001,17 @@ run these steps:
    the <a data-lt="structured field token">token</a> <code>prefetch</code>) in
    <var>httpRequest</var>'s <a for=request>header list</a>.
 
-   <li><p>If <var>httpRequest</var>'s <a for=request>header list</a>
-   <a for="header list">does not contain</a> `<code>User-Agent</code>`, then user agents should
-   <a for="header list">append</a> (`<code>User-Agent</code>`,
-   <a>default `<code>User-Agent</code>` value</a>) to <var>httpRequest</var>'s
-   <a for=request>header list</a>.
+   <li>
+    <p>If <var>httpRequest</var>'s <a for=request>header list</a> <a
+    for="header list">does not contain</a> `<code>User-Agent</code>`, then user agents should:
+
+    <ol>
+     <li><p>Let <var>userAgent</var> be <var>httpRequest</var>'s <a for=request>client</a>'s
+     <a>environment default `<code>User-Agent</code>` value</a>.
+
+     <li><p><a for="header list">Append</a> (`<code>User-Agent</code>`, <var>userAgent</var>) to
+     <var>httpRequest</var>'s <a for=request>header list</a>.
+    </ol>
 
    <li><p>If <var>httpRequest</var>'s <a for=request>cache mode</a> is "<code>default</code>" and
    <var>httpRequest</var>'s <a for=request>header list</a> <a for="header list">contains</a>