diff --git a/composer.json b/composer.json
index f5fc014..caf894d 100644
--- a/composer.json
+++ b/composer.json
@@ -15,7 +15,7 @@
         "php": ">=5.3.0"
     },
     "require-dev": {
-        "phpunit/phpunit": ">=5.7"
+        "phpunit/phpunit": "~5.7"
     },
     "autoload": {
         "psr-4": {