diff --git a/composer.json b/composer.json
index 748ed2e..9c284c3 100644
--- a/composer.json
+++ b/composer.json
@@ -5,7 +5,10 @@
     "homepage": "https://github.com/Icinga/icingaweb2-module-reactbundle",
     "license": "MIT",
     "config": {
-        "sort-packages": true
+        "sort-packages": true,
+        "platform": {
+            "php": "5.6.3"
+        }
     },
     "support": {
         "issues": "https://github.com/Icinga/icingaweb2-module-reactbundle/issues"