diff --git a/piwik.php b/piwik.php
index 4346bfb18566e340a5fda27d8d8c77e0891be07b..65fa14cc68c5adea2a245862cfcd58e3bd8c36f5 100644
--- a/piwik.php
+++ b/piwik.php
@@ -15,7 +15,7 @@ use Piwik\Tracker;
 $GLOBALS['PIWIK_TRACKER_DEBUG_FORCE_SCHEDULED_TASKS'] = false;
 define('PIWIK_ENABLE_TRACKING', true);
 
-if (!defined(PIWIK_DOCUMENT_ROOT)) {
+if (!defined('PIWIK_DOCUMENT_ROOT')) {
     define('PIWIK_DOCUMENT_ROOT', dirname(__FILE__) == '/' ? '' : dirname(__FILE__));
 }