After firing this command in command line php bin/magento setup:di:compile I am getting this error:

Cannot declare interface Magento\Framework\App\DeploymentConfig\Writer\FormatterInterface, because the name is already in use in /var/www/html/vendor/magento/framework/App/DeploymentConfig/Writer/FormatterInterface.php on line 9

Can you have a best solution for me?


  • Is there any custom extension? Commented Dec 24, 2016 at 3:25
  • just try with remove var folder from root and run again. Commented Dec 24, 2016 at 5:17

2 Answers 2


Please try to remove all the directories inside var/generation folder and then run following command :

php bin/magento cache:flush

After that run your command you will be succeed.

  • Thank for your idea!
    – Peter
    Commented Jan 20, 2017 at 3:29
  • Most welcome :) Commented Jan 9, 2019 at 11:09

Make sure that in your interface and also the interface that Magento says you are re-declaring, that you have declared the namespace at the top of both classes. This has happened to me before and that is usually the reason.


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