diff --git a/composer.json b/composer.json
index 95d6b0f..224066b 100644
--- a/composer.json
+++ b/composer.json
@@ -27,6 +27,6 @@
     "require-dev": {
         "react/http": "^0.4.1",
         "react/socket-client": "^0.4.3",
-        "phpunit/phpunit": "5.7"
+        "phpunit/phpunit": "4.8.*"
     }
 }