diff --git a/composer.json b/composer.json
index 87430df..f7cc815 100644
--- a/composer.json
+++ b/composer.json
@@ -7,7 +7,7 @@
         "composer/installers": "~1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.5",
+        "phpunit/phpunit": "^5.7.21 || ^6.5 || ^7.5",
         "phpcompatibility/php-compatibility": "*",
         "squizlabs/php_codesniffer": "3.*",
         "wp-coding-standards/wpcs": "^2.3.0"