diff --git a/composer.json b/composer.json
index 8cc69e7c..9692f18b 100644
--- a/composer.json
+++ b/composer.json
@@ -24,7 +24,7 @@
     }
   },
   "require-dev": {
-    "phpunit/phpunit": "*",
+    "phpunit/phpunit": "<=7.5",
     "symfony/var-dumper": "*"
   }
 }