diff --git a/composer.json b/composer.json
index ee0810f..f63eed2 100644
--- a/composer.json
+++ b/composer.json
@@ -27,5 +27,10 @@
         "amphp/phpunit-util": "^1.0",
         "friendsofphp/php-cs-fixer": "^2.9",
         "phpunit/phpunit": "^6.5"
+    },
+    "config": {
+        "platform": {
+            "php": "7.0.0"
+        }
     }
 }