diff --git a/composer.json b/composer.json
index 5a67a02..5a43df2 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
     },
     "require": {
         "php": "^7.0",
-        "symfony/yaml": "^3.2",
+        "symfony/yaml": "^3.2|^4.0",
         "nesbot/carbon": "^1.22",
         "psr/http-message": "^1.0",
         "php-http/client-common": "^1.1",