diff --git a/composer.json b/composer.json
index d6740aa4..d8d11125 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,7 @@
         "defuse/php-encryption": "^2.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8 || ^5.0",
+        "phpunit/phpunit": "^4.8.38 || ^5.7.21",
         "zendframework/zend-diactoros": "^1.0"
     },
     "repositories": [