diff --git a/composer.json b/composer.json
index 937dd74..8a31eac 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
     "pimple/pimple": "^3.0",
     "monolog/monolog": "^1.17",
     "symfony/validator": "^3.0",
-    "symfony/yaml": "^2.8 | ^3.0",
+    "symfony/yaml": "^2.8 | ^3.0 | ^4.0",
     "ext-json": "*"
   },
   "require-dev": {