const = BASE_PATH. '/ folder' does not work on server

Hello. My code is:

In index.php

define('BASE_PATH', realpath(__DIR__.'/../')); 

In the class Config.php:

 class Config { const ERROR_PATH = BASE_PATH.'/runtime/errors'; } 

In locale everything works. And in the server error:

 Parse error: syntax error, unexpected '.', expecting ',' or ';' in /home/xxx/xxx/Core/Config.php on line 106 

How can I fix this?