diff --git a/index.html b/index.html
index 2efdb924..2408aaca 100644
--- a/index.html
+++ b/index.html
@@ -566,7 +566,7 @@ <h3>
           historical reasons.
         </div>
         <pre class="idl">
-          [Constructor]
+          [Constructor, Exposed=Window]
           interface BeforeInstallPromptEvent : Event {
               Promise&lt;PromptResponseObject&gt; prompt();
           };