diff --git a/composer.json b/composer.json
index 4047626f..edb8f0d2 100644
--- a/composer.json
+++ b/composer.json
@@ -69,6 +69,11 @@
             "vendor/bin/ecs check src/ spec/ --fix"
         ]
     },
+    "config": {
+        "allow-plugins": {
+            "symfony/flex": true
+        }
+    },
     "extra": {
         "branch-alias": {
             "dev-master": "1.1-dev"