diff --git a/README b/README
index 0ae8a4e..86270df 100644
--- a/README
+++ b/README
@@ -9,6 +9,7 @@ Will Rossiter
 
 Requirements
 -----------------------------------------------
+SilverStripe 2.4 or newer
 
 Documentation
 -----------------------------------------------
diff --git a/code/GoogleSitemap.php b/code/GoogleSitemap.php
index e706301..8181f54 100755
--- a/code/GoogleSitemap.php
+++ b/code/GoogleSitemap.php
@@ -62,9 +62,9 @@ class GoogleSitemap extends Controller {
 						// The one field that isn't easy to deal with in the template is
 						// Change frequency, so we set that here.
 						$properties = $page->toMap();
-						$created = new SSDatetime();
+						$created = new SS_Datetime();
 						$created->value = $properties['Created'];
-						$now = new SSDatetime();
+						$now = new SS_Datetime();
 						$now->value = date('Y-m-d H:i:s');
 						$versions = $properties['Version'];
 						$timediff = $now->format('U') - $created->format('U');