diff --git a/tests/composer.json b/tests/composer.json
index 6202958c9..8ca93a75c 100644
--- a/tests/composer.json
+++ b/tests/composer.json
@@ -34,5 +34,8 @@
     "branch-alias": {
       "dev-master": "3.1.x-dev"
     }
+  },
+  "require": {
+    "phpunit/phpunit": "^6.4.1 || ^4.6.6"
   }
 }