diff --git a/composer.json b/composer.json
index b1e1d25..6ff6506 100644
--- a/composer.json
+++ b/composer.json
@@ -34,7 +34,7 @@
         "react/stream": "^1.4"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.6 || ^5.7 || ^4.8.36",
+        "phpunit/phpunit": "^9.6 || ^8.5 || ^5.7 || ^4.8.36",
         "react/async": "^4.3 || ^3.3 || ^2",
         "react/promise-stream": "^1.4",
         "react/promise-timer": "^1.11"