diff --git a/composer.json b/composer.json
index 4924c2e..15913c6 100644
--- a/composer.json
+++ b/composer.json
@@ -30,7 +30,7 @@
         "react/promise": "^3.0 || ^2.0 || ^1.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.6 || ^5.7 || ^4.8.36"
+        "phpunit/phpunit": "^9.6 || ^8.5 || ^5.7 || ^4.8.36"
     },
     "autoload": {
         "psr-4": {