diff --git a/index.html b/index.html
index 8c7c6708..55560ab8 100644
--- a/index.html
+++ b/index.html
@@ -10575,7 +10575,8 @@ <h3>User Prompt Handler</h3>
 <p>To <dfn>serialize the user prompt handler</dfn>:
 
 <ol class=algorithm>
- <li><p>If the <a>user prompt handler</a> is null, return null.
+ <li><p>If the <a>user prompt handler</a> is null, return
+ "<code>dismiss and notify</code>".
 
  <li><p>If the <a>user prompt handler</a> has [=map/size=] 1,
  and <a>user prompt handler</a> [=list/contains=]