diff --git a/composer.json b/composer.json
index ff2702e..2e1a580 100644
--- a/composer.json
+++ b/composer.json
@@ -30,7 +30,7 @@
   "require-dev": {
     "friendsofphp/php-cs-fixer": "^2.15",
     "phpbench/phpbench": "^0.16.9",
-    "phpunit/phpunit": "^5.0|^7.0"
+    "phpunit/phpunit": "^5.0|^7.0|^8.0"
   },
   "support": {
     "issues": "https://github.com/rayne/wz2008-graph/issues",