diff --git a/api/HTMLMediaElement.json b/api/HTMLMediaElement.json
index e969ca9fa24a24..dbce14a18a5282 100644
--- a/api/HTMLMediaElement.json
+++ b/api/HTMLMediaElement.json
@@ -3571,6 +3571,7 @@
       "waitingforkey_event": {
         "__compat": {
           "description": "`waitingforkey` event",
+          "mdn_url": "https://developer.mozilla.org/docs/Web/API/HTMLMediaElement/waitingforkey_event",
           "spec_url": "https://w3c.github.io/encrypted-media/#dom-htmlmediaelement-onwaitingforkey",
           "support": {
             "chrome": {