diff --git a/lib/web/websocket/events.js b/lib/web/websocket/events.js
index 3f2cf61ada9..5fd2a6568a3 100644
--- a/lib/web/websocket/events.js
+++ b/lib/web/websocket/events.js
@@ -143,13 +143,13 @@ class ErrorEvent extends Event {
     const prefix = 'ErrorEvent constructor'
     webidl.argumentLengthCheck(arguments, 1, prefix)
 
-    super(type, eventInitDict)
-    webidl.util.markAsUncloneable(this)
-
     type = webidl.converters.DOMString(type, prefix, 'type')
     eventInitDict = webidl.converters.ErrorEventInit(eventInitDict ?? {})
 
+    super(type, eventInitDict)
+
     this.#eventInit = eventInitDict
+    webidl.util.markAsUncloneable(this)
   }
 
   get message () {