diff --git a/composer.json b/composer.json
index 4b82aa2..305fb3c 100644
--- a/composer.json
+++ b/composer.json
@@ -23,6 +23,6 @@
         "php": ">=5.6.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "5.7.27"
+        "phpunit/phpunit": "9.5.21"
     }
 }