diff --git a/code/Forms/SiteTreeURLSegmentField.php b/code/Forms/SiteTreeURLSegmentField.php
index bd26ca71..2e3a44b0 100644
--- a/code/Forms/SiteTreeURLSegmentField.php
+++ b/code/Forms/SiteTreeURLSegmentField.php
@@ -82,7 +82,7 @@ class SiteTreeURLSegmentField extends TextField
         $page->URLSegment = $page->generateURLSegment($request->getVar('value'));
         $count = 2;
         while (!$page->validURLSegment()) {
-            $page->URLSegment = preg_replace('/-[0-9]+$/', null, $page->URLSegment) . '-' . $count;
+            $page->URLSegment = preg_replace('/-[0-9]+$/', '', $page->URLSegment) . '-' . $count;
             $count++;
         }
 
diff --git a/code/Model/SiteTree.php b/code/Model/SiteTree.php
index c633962c..458ec9c5 100755
--- a/code/Model/SiteTree.php
+++ b/code/Model/SiteTree.php
@@ -1652,7 +1652,7 @@ class SiteTree extends DataObject implements PermissionProvider, i18nEntityProvi
         // Ensure that this object has a non-conflicting URLSegment value.
         $count = 2;
         while (!$this->validURLSegment()) {
-            $this->URLSegment = preg_replace('/-[0-9]+$/', null, $this->URLSegment) . '-' . $count;
+            $this->URLSegment = preg_replace('/-[0-9]+$/', '', $this->URLSegment) . '-' . $count;
             $count++;
         }