Symfony2:类声明可能不会嵌套在FatalErrorException.php中

When I get a fatal error in my Symfony 2.3.7 project I get a blank page and not a symfony error page in my dev-environment.

When I check the error-log of the server I can see the error that caused the fatal error and another error:

PHP Fatal error: Class declarations may not be nested in /vendor/symfony/symfony/src/Symfony/Component/Debug/Exception/FatalErrorException.php on line 20

I have no idea what could cause this behavior. This is a normal, standard Symfony2 installation.

I 've updated my vendors, cleared the cache multiple times, ... but I can't seem to find the problem.

Has anybody experienced this before or have a clue what could be wrong?