In the composer.json file I added "drupal/core": "~8.4" to the required section. When I run composer update drupal/core --with-all-dependencies, I get the following output.

Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Problem 1

  • drupal/core 8.4.0 conflicts with acquia/blt-project

Why does Drupal 8.4 conflict with acquia/blt-project?

  • 1
    Read drupal.org/docs/8/update/update-core-via-composer#known-issues and update your question - or add an answer yourself ;-)
    – hansfn
    Commented Sep 18, 2018 at 17:01
  • Why don't you simply composer update --with-dependencies? I do that every now and then at least once a week and never had any problem.
    – leymannx
    Commented Sep 18, 2018 at 18:14
  • I’ve been googling this conflict for a day now but haven’t found a solution. This conflict is more about acquia/blt issue I think. Yep done that command also without any luck.
    – mana
    Commented Sep 18, 2018 at 21:01
  • 1
    Is there an update to the module that can be run first to avoid the conflict? Commented Sep 19, 2018 at 0:22
  • 2
    Looks like the 8.9.x version is in EOL and only has support for <= D8.5.. look at the 8.8.x or 9.x version for support of D8.4. Have a look at the 9.x README.md github.com/acquia/blt/blob/9.x/docs/README.md Commented Sep 19, 2018 at 3:02

1 Answer 1


The problem was a line in my composer.json file which is prevent the upgrade from happening.

In the "conflict" section, there's a line "drupal/core": ">=8.4.0-alpha1" I have to remove that line and also run the following commands to complete the upgrade.

composer update --lock
composer require acquia/lightning:^3.0 acquia/blt:^8.9 --no-update
composer update acquia/lightning --with-all-dependencies

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