diff --git a/composer.json b/composer.json
index 64fe3de..573ffe6 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
     ],
     "require": {
         "php": ">=5.6.0",
-        "symfony/yaml": "2.*|3.*"
+        "symfony/yaml": "2.*|3.*|4.*"
     },
     "require-dev": {
         "phpunit/phpunit": "5.*",