diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 71efcda07..bad4b4c71 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -135,6 +135,9 @@ jobs:
             - name: "Add PHPUnit matcher"
               run: echo "::add-matcher::${{ runner.tool_cache }}/phpunit.json"
 
+            - name: "Allow the Flex Plugin"
+              run: composer global config --no-plugins allow-plugins.symfony/flex true
+
             - name: "Require symfony/flex"
               run: composer global require --no-progress --no-scripts --no-plugins symfony/flex
 
diff --git a/appveyor.yml b/appveyor.yml
index 492d4a200..0f398933d 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -53,6 +53,7 @@ install:
     - del composer.phar
     - rename composer-stable.phar composer.phar
     - cd C:\projects\maker-bundle
+    - composer global config --no-plugins allow-plugins.symfony/flex true
     - composer global require --no-progress --no-scripts --no-plugins symfony/flex
     - IF %dependencies%==highest appveyor-retry composer update --no-progress --no-suggest --ansi
     - composer install --no-interaction --no-progress --ansi --no-scripts --working-dir=tools/twigcs