diff --git a/composer.json b/composer.json
index f31d1e7..1b0028e 100644
--- a/composer.json
+++ b/composer.json
@@ -24,6 +24,7 @@
         }
     },
     "require-dev": {
-        "phpunit/phpunit": "~4.0 || ^9"
+        "phpunit/phpunit": "~4.0 || ^9",
+        "symfony/polyfill": "^1.30"
     }
 }