diff --git a/composer.json b/composer.json
index 0937440..37c8712 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
         "php": ">=5.3.2"
     },
     "require-dev": {
-        "phpunit/phpunit": ">=4.8.35 <9"
+        "phpunit/phpunit": ">=4.8.35"
     },
     "suggest": {
         "ext-mbstring": "It can support the multiple bytes string length."