diff --git a/core/kernel/impl/class.ApiModelOO.php b/core/kernel/impl/class.ApiModelOO.php
index f7fdfa9b6..e4652352d 100644
--- a/core/kernel/impl/class.ApiModelOO.php
+++ b/core/kernel/impl/class.ApiModelOO.php
@@ -425,7 +425,7 @@ private function addCoreNamespaces(DOMElement $root): void
         }
 
         $this->customNamespacesCounter = 0;
-        $this->addCustomNamespace($root, ROOT_URL);
+        $this->addCustomNamespace($root, LOCAL_NAMESPACE);
     }
 
     /**