diff --git a/phpBB/phpbb/db/migration/data/v310/allow_cdn.php b/phpBB/phpbb/db/migration/data/v310/allow_cdn.php
index 2570998643..0b79ac77f9 100644
--- a/phpBB/phpbb/db/migration/data/v310/allow_cdn.php
+++ b/phpBB/phpbb/db/migration/data/v310/allow_cdn.php
@@ -11,6 +11,11 @@ namespace phpbb\db\migration\data\v310;
 
 class allow_cdn extends phpbb_db_migration
 {
+	public function effectively_installed()
+	{
+		return isset($this->config['allow_cdn']);
+	}
+
 	static public function depends_on()
 	{
 		return array(