diff --git a/code/extensions/GroupSubsites.php b/code/extensions/GroupSubsites.php
index 41667415..cdb18c63 100644
--- a/code/extensions/GroupSubsites.php
+++ b/code/extensions/GroupSubsites.php
@@ -46,7 +46,8 @@ public function requireDefaultRecords()
             return;
         }
         // Migration for Group.SubsiteID data from when Groups only had a single subsite
-        $schema = $this->owner::getSchema();
+        $ownerClass = get_class($this->owner);
+        $schema = $ownerClass::getSchema();
         $groupFields = DB::field_list($schema->tableName(Group::class));
 
         // Detection of SubsiteID field is the trigger for old-style-subsiteID migration