diff --git a/composer.json b/composer.json
index ff13cf6..5145d0a 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
     "require-dev": {
         "ext-parallel": "*",
         "react-parallel/stubs": "^1.2",
-        "wyrihaximus/async-test-utilities": "^8.0.5"
+        "wyrihaximus/async-test-utilities": "^8.0.5 || ^9.0.0"
     },
     "autoload": {
         "psr-4": {