diff --git a/composer.json b/composer.json
index a53aaae..4ca39aa 100644
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
         "ext-json": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "~9",
+        "phpunit/phpunit": ">=8 <10",
         "squizlabs/php_codesniffer": "^3.5.8"
     },
     "autoload": {