diff --git a/composer.json b/composer.json
index cbbaca0..15e30b4 100644
--- a/composer.json
+++ b/composer.json
@@ -34,7 +34,7 @@
         "php": ">=5.5"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6",
+        "phpunit/phpunit": "8.5.52",
         "squizlabs/php_codesniffer": "^3.5"
     },
     "suggest": {