diff --git a/composer.json b/composer.json
index d1407f8..f32fd06 100644
--- a/composer.json
+++ b/composer.json
@@ -10,7 +10,7 @@
         "keepachangelog"
     ],
     "require-dev": {
-        "phpunit/phpunit": "4.*"
+        "phpunit/phpunit": "^6.0"
     },
     "license": "MIT",
     "authors": [