diff --git a/composer.json b/composer.json
index 37fa7ab..5089034 100644
--- a/composer.json
+++ b/composer.json
@@ -35,7 +35,7 @@
     "require-dev": {
         "phacility/arcanist": "dev-master#5eda40337bb4135ca4929617602686302edc7cc0",
         "composer/composer": "^1.4",
-        "phpunit/phpunit": "^5.0",
+        "phpunit/phpunit": "^5.0 || ^6.0",
         "phacility/libphutil": "dev-master#276f6d304b69767d48f88f65484ce310ee2cf3af",
         "friendsofphp/php-cs-fixer": "^2.2"
     },