diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5ea5e489..e69f6243 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Changed
 
+- Mark `OutputFormatter` as `@internal` (#896)
 - Mark `Selector::isValid()` as `@internal` (#1037)
 - Mark parsing-related methods of most CSS elements as `@internal` (#908)
 - Mark `OutputFormat::nextLevel()` as `@internal` (#901)
diff --git a/src/OutputFormat.php b/src/OutputFormat.php
index 60c63a05..ad82395a 100644
--- a/src/OutputFormat.php
+++ b/src/OutputFormat.php
@@ -363,12 +363,15 @@ public function beLenient()
 
     /**
      * @return OutputFormatter
+     *
+     * @internal since 8.8.0
      */
     public function getFormatter()
     {
         if ($this->oFormatter === null) {
             $this->oFormatter = new OutputFormatter($this);
         }
+
         return $this->oFormatter;
     }
 
diff --git a/src/OutputFormatter.php b/src/OutputFormatter.php
index 3844383d..a436ee3b 100644
--- a/src/OutputFormatter.php
+++ b/src/OutputFormatter.php
@@ -5,6 +5,9 @@
 use Sabberworm\CSS\Comment\Commentable;
 use Sabberworm\CSS\Parsing\OutputException;
 
+/**
+ * @internal since 8.8.0
+ */
 class OutputFormatter
 {
     /**