| Q | A | ---------------- | ----- | Bug report? | yes | Feature request? | no | BC Break report? | no | RFC? | no | Symfony version | 3.4.0-RC2 but I guess it is the same in 3.3.x Hello, We have an issue while we cannot use old `DefinitionDecorator` class: > Fatal error: Uncaught Error: Class 'Symfony\Component\DependencyInjection\DefinitionDecorator' not found with the `optimize` option of composer: `composer dump-autoload --optimize` I have no idea how to fix it but I'm available to make a PR if anyone else have an idea ! Related PR: - original fix : https://github.com/symfony/symfony/pull/20968 - latest fix : https://github.com/symfony/symfony/pull/22657