diff --git a/server/composer.json b/server/composer.json
index 33ac9431..81592050 100755
--- a/server/composer.json
+++ b/server/composer.json
@@ -9,6 +9,6 @@
         "ezyang/htmlpurifier": "^4.8"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.4.3"
+        "phpunit/phpunit": "^5.7"
     }
 }