diff --git a/tools/php-unit/composer.json b/tools/php-unit/composer.json
index 2bce152..51259ef 100644
--- a/tools/php-unit/composer.json
+++ b/tools/php-unit/composer.json
@@ -1,5 +1,5 @@
 {
     "require": {
-        "phpunit/phpunit": "^8 || ^9"
+        "phpunit/phpunit": "^9.5.6"
     }
 }