diff --git a/composer.json b/composer.json
index f18d7ce..e45a96f 100644
--- a/composer.json
+++ b/composer.json
@@ -26,7 +26,7 @@
     }
   },
   "require-dev": {
-    "phpunit/phpunit": "^8.0",
+    "phpunit/phpunit": "^5.5",
     "mockery/mockery": "^0.9.5"
   }
 }