diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index c6d63e13f4..0be3e289e2 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -3475,7 +3475,15 @@ function phpbb_filter_root_path($errfile)
 
 	if (empty($root_path))
 	{
-		$root_path = $phpbb_filesystem->realpath(dirname(__FILE__) . '/../');
+		if ($phpbb_filesystem)
+		{
+			$root_path = $phpbb_filesystem->realpath(dirname(__FILE__) . '/../');
+		}
+		else
+		{
+			$filesystem = new \phpbb\filesystem\filesystem();
+			$root_path = $filesystem->realpath(dirname(__FILE__) . '/../');
+		}
 	}
 
 	return str_replace(array($root_path, '\\'), array('[ROOT]', '/'), $errfile);