diff --git a/composer.json b/composer.json
index a09abe9..4c938ea 100644
--- a/composer.json
+++ b/composer.json
@@ -31,7 +31,7 @@
     "php-parallel-lint/php-parallel-lint": "^1.2",
     "phpro/grumphp-shim": "^0.19.1",
     "phpstan/phpstan": "^0.12.31",
-    "phpunit/phpunit": "^8.5",
+    "phpunit/phpunit": "^8.5 || ^9.0",
     "roave/security-advisories": "dev-master",
     "sensiolabs/security-checker": "^6.0",
     "squizlabs/php_codesniffer": "^3.5"