diff --git a/phpBB/includes/acp/acp_styles.php b/phpBB/includes/acp/acp_styles.php
index f5bb241e57..ff95ddeec0 100644
--- a/phpBB/includes/acp/acp_styles.php
+++ b/phpBB/includes/acp/acp_styles.php
@@ -34,7 +34,7 @@ class acp_styles
 		$bitfield->set(9);
 		$bitfield->set(11);
 		$bitfield->set(12);
-		define('TEMPLATE_BITFIELD', $bitfield->data);
+		define('TEMPLATE_BITFIELD', $bitfield->get_base64());
 
 		$user->add_lang('acp/styles');