diff --git a/lib/websocket.js b/lib/websocket.js
index baf493458..7f1e3bcfa 100644
--- a/lib/websocket.js
+++ b/lib/websocket.js
@@ -128,7 +128,7 @@ class WebSocket extends EventEmitter {
    */
   /* istanbul ignore next */
   get onerror() {
-    return null;
+    return undefined;
   }
 
   /* istanbul ignore next */