diff --git a/_config.php b/_config.php
index eec9e6af..6e13b509 100644
--- a/_config.php
+++ b/_config.php
@@ -9,8 +9,12 @@ use SilverStripe\Assets\File;
  * - CMS_DIR: Path relative to webroot, e.g. "cms"
  * - CMS_PATH: Absolute filepath, e.g. "/var/www/my-webroot/cms"
  */
-define('CMS_DIR', 'cms');
-define('CMS_PATH', BASE_PATH . '/' . CMS_DIR);
+define('CMS_PATH', realpath(__DIR__));
+if(strpos(CMS_PATH, BASE_PATH) === 0) {
+	define('CMS_DIR', trim(substr(CMS_PATH, strlen(BASE_PATH)), '/'));
+} else {
+	throw new Exception("Path error: CMS_PATH " . CMS_PATH . " not within BASE_PATH " . BASE_PATH);
+}
 
 /**
  * Register the default internal shortcodes.