diff --git a/composer.json b/composer.json
index b55e13785..d0496a175 100644
--- a/composer.json
+++ b/composer.json
@@ -36,7 +36,8 @@
     "minimum-stability" : "stable",
     "require": {
         "php": ">=5.3.9",
-        "pdepend/pdepend": "^2.2"
+        "pdepend/pdepend": "^2.2",
+        "ext-xml": *
     },
     "require-dev": {
         "phpunit/phpunit": "^4.0",