diff --git a/composer.json b/composer.json
index a1bfda41..800e0f1a 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,7 @@
         "paragonie/random_compat": "^1.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "4.8.*"
+        "phpunit/phpunit": "~5.2"
     },
     "repositories": [
         {