diff --git a/composer.json b/composer.json
index 3bcf732..458873a 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
     "thecodingmachine/safe": "^2.4.0"
   },
   "require-dev": {
-    "wyrihaximus/async-test-utilities": "^8.0.0"
+    "wyrihaximus/async-test-utilities": "^8.0.0 || ^9.0.0"
   },
   "autoload": {
     "psr-4": {