diff --git a/docs/index.bs b/docs/index.bs
index bd698770..695a1567 100644
--- a/docs/index.bs
+++ b/docs/index.bs
@@ -3352,6 +3352,9 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
 
       1. Let |baseURL| be |serviceWorker|'s [=service worker/script url=].
       1. Return the result of [=building a URLPattern from a Web IDL value=] |rawPattern| given |baseURL| and |serviceWorker|'s [=service worker/global object=]'s [=relevant realm=].
+
+      Note: Since the [=building a URLPattern from a Web IDL value=] algorithm actually do not depend on the realm, it is  fine to call the algorithm here even if the [=service worker/global object=] may not be ready.
+
   </section>
 
   <section algorithm>