diff --git a/composer.json b/composer.json
index ae09bf2..ccaf67f 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
     ],
     "require": {},
     "require-dev": {
-        "phpunit/phpunit": "^6.5",
+        "phpunit/phpunit": "^6.5 || ^7 || ^8 || ^9",
         "squizlabs/php_codesniffer": "^3.3",
         "satooshi/php-coveralls": "^2.0"
     },