diff --git a/Classes/Domain/Index/AbstractIndexer.php b/Classes/Domain/Index/AbstractIndexer.php
index 7eae615..0172c12 100644
--- a/Classes/Domain/Index/AbstractIndexer.php
+++ b/Classes/Domain/Index/AbstractIndexer.php
@@ -208,5 +208,5 @@ abstract class AbstractIndexer implements IndexerInterface
 
     abstract protected function getDocumentName(): string;
 
-    abstract public function getDocumentIdentifier($identifier): string;
+    abstract protected function getDocumentIdentifier($identifier): string;
 }
diff --git a/Classes/Domain/Index/TcaIndexer.php b/Classes/Domain/Index/TcaIndexer.php
index e1b03b7..0c1d00d 100644
--- a/Classes/Domain/Index/TcaIndexer.php
+++ b/Classes/Domain/Index/TcaIndexer.php
@@ -89,7 +89,7 @@ class TcaIndexer extends AbstractIndexer
         return $this->tcaTableService->getTableName();
     }
 
-    public function getDocumentIdentifier($identifier): string
+    protected function getDocumentIdentifier($identifier): string
     {
         return $this->getDocumentName() . '-' . $identifier;
     }
diff --git a/Documentation/source/changelog/0.1.0/2018-changed-interfaces.rst b/Documentation/source/changelog/0.1.0/2018-changed-interfaces.rst
index 669c776..93d5c81 100644
--- a/Documentation/source/changelog/0.1.0/2018-changed-interfaces.rst
+++ b/Documentation/source/changelog/0.1.0/2018-changed-interfaces.rst
@@ -15,7 +15,7 @@ Some interfaces and abstract classes have been adjusted:
 
 ``Codappix\SearchCore\Domain\Index\AbstractIndexer``:
 
-   * New method ``abstract public function getDocumentIdentifier($identifier): string;``
+   * New method ``abstract protected function getDocumentIdentifier($identifier): string;``
 
 ``Codappix\SearchCore\Connection\SearchRequestInterface``: