diff --git a/composer.json b/composer.json
index 407ac08..a06ab71 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
         "php": ">=5.4.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^8"
+        "phpunit/phpunit": "^9"
     },
     "autoload": {
         "psr-4": {