diff --git a/composer.json b/composer.json
index cb1137b..c9ed7ce 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
     "require-dev": {
         "overtrue/phplint": "^1.1",
         "phpstan/phpstan-shim": "^0.9|^0.10|^0.11",
-        "phpunit/phpunit": "^7",
+        "phpunit/phpunit": "^6|^7",
         "squizlabs/php_codesniffer": "^3.4"
     },
     "scripts": {