diff --git a/code/Model/SiteTree.php b/code/Model/SiteTree.php
index 614630f6..fef4ea9a 100755
--- a/code/Model/SiteTree.php
+++ b/code/Model/SiteTree.php
@@ -2124,7 +2124,7 @@ class SiteTree extends DataObject implements PermissionProvider, i18nEntityProvi
 
             $fields->addFieldToTab(
                 "Root.Main",
-                new LiteralField("ObsoleteWarningHeader", "<p class=\"message warning\">$obsoleteWarning</p>"),
+                LiteralField::create("ObsoleteWarningHeader", "<p class=\"alert alert-warning\">$obsoleteWarning</p>"),
                 "Title"
             );
         }