diff --git a/composer.json b/composer.json
index d2c15b3..d952a62 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
     "phpseclib/phpseclib": ">=2.0.0 <=2.0.4"
   },
   "require-dev": {
-    "phpunit/phpunit": "~4.0"
+    "phpunit/phpunit": "~5.0"
   },
   "suggest": {
     "ext-mcrypt": "required if you use encryption cast5"