diff --git a/spec/service_worker/index.html b/spec/service_worker/index.html
index 854fae69..050a2ec3 100644
--- a/spec/service_worker/index.html
+++ b/spec/service_worker/index.html
@@ -823,6 +823,7 @@ <h1><code>focus()</code></h1>
         <li>Let <var>promise</var> be a new <a href="https://people.mozilla.org/~jorendorff/es6-draft.html#sec-promise-objects">promise</a>.</li>
         <li>Run these steps in parallel:
           <ol>
+            <li>If this algorithm is not <a href="https://html.spec.whatwg.org/multipage/browsers.html#allowed-to-show-a-popup">allowed to show a popup</a>, return a <a href="https://people.mozilla.org/~jorendorff/es6-draft.html#sec-promise-objects">promise</a> rejected with a "<code><a href="http://heycam.github.io/webidl/#invalidaccesserror">InvalidAccessError</a></code>" exception.</li>
             <li>Let <var>browsingContext</var> be the <a href="https://dom.spec.whatwg.org/#context-object">context object</a>'s associated <a href="#dfn-service-worker-client-client">service worker client</a>'s <a href="https://html.spec.whatwg.org/multipage/webappapis.html#global-object">global object</a>'s <a href="https://html.spec.whatwg.org/multipage/browsers.html#browsing-context">browsing context</a>.</li>
             <li><a href="https://html.spec.whatwg.org/multipage/webappapis.html#queue-a-task">Queue a task</a> to run the following substeps on the <a href="https://dom.spec.whatwg.org/#context-object">context object</a>'s associated <a href="#dfn-service-worker-client-client">service worker client</a>'s <a href="https://html.spec.whatwg.org/multipage/webappapis.html#responsible-event-loop">responsible event loop</a> using the <a href="https://html.spec.whatwg.org/#user-interaction-task-source">user interaction task source</a>:
               <ol>