diff --git a/composer.json b/composer.json
index 33140dc..b12dde9 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
     "ext-curl": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "3.7.*",
+    "phpunit/phpunit": "^5.7",
     "squizlabs/php_codesniffer": "~2.1"
   },
   "autoload": {