diff --git a/tests/adapters/jquery/manual/nockeditor.html b/tests/adapters/jquery/manual/nockeditor.html
index 8cd0556e2f0..bdc9e87bf92 100644
--- a/tests/adapters/jquery/manual/nockeditor.html
+++ b/tests/adapters/jquery/manual/nockeditor.html
@@ -1,3 +1,4 @@
 <script>
-	delete window.CKEDITOR;
+	// Can't use `delete` because IE8 fails. #13177
+	window.CKEDITOR = undefined;
 </script>