diff --git a/composer.json b/composer.json
index fccc097..3bca984 100644
--- a/composer.json
+++ b/composer.json
@@ -26,7 +26,7 @@
         "php": "^7.1.3"
     },
     "require-dev": {
-        "phpunit/phpunit": "7.5.20"
+        "phpunit/phpunit": "9.1.4"
     },
     "autoload": {
         "psr-4": {