diff --git a/composer.json b/composer.json
index 4938c7d..a2fbd01 100755
--- a/composer.json
+++ b/composer.json
@@ -15,7 +15,7 @@
   "require": {
     "php": "^7.1",
     "psr/http-message": "^1.0",
-    "phpunit/phpunit": "^7.0",
+    "phpunit/phpunit": "^6.0 | ^7.0",
     "justinrainbow/json-schema": "~2.0"
   },
   "autoload": {