diff --git a/composer.json b/composer.json
index 280686e..589ac5c 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
         "psr/log": "~1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "4.8.*",
+        "phpunit/phpunit": "^4.0|^5.0",
         "satooshi/php-coveralls": "~0.7.1"
     },
     "autoload": {