diff --git a/composer.json b/composer.json
index bfb2982ea..38bc7dc42 100644
--- a/composer.json
+++ b/composer.json
@@ -22,7 +22,7 @@
 		"ext-mcrypt": "*"
 	},
 	"require-dev": {
-		"phpunit/phpunit": "^5.0",
+		"phpunit/phpunit": "<6.0.0",
 		"cakephp/cakephp-codesniffer": "^1.0.0"
 	},
 	"config": {