diff --git a/fetch.bs b/fetch.bs
index 0de8d7441..61e6b260b 100644
--- a/fetch.bs
+++ b/fetch.bs
@@ -5039,6 +5039,10 @@ steps. They return a <a for=/>response</a>.
    <li><p><a abstract-op lt="append the Fetch metadata headers for a request">Append the Fetch metadata headers for <var>httpRequest</var></a>.
    [[!FETCH-METADATA]]
 
+   <li><p>If <var>httpRequest</var>'s <a for=request>initiator</a> is "<code>prefetch</code>", then
+   <a for="header list">append</a> (`<code>Sec-Purpose</code>`, "<code>prefetch</code>") 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
    <a for="header list">append</a> (`<code>User-Agent</code>`,