diff --git a/CHANGELOG.md b/CHANGELOG.md
index 362a65466..9f34e14b6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@ Please also have a look at our
 
 ### Changed
 
+- Mark `OutputFormatter` as `@internal` (#896)
 - Make `Selector` a `Renderable` (#1017)
 - Mark `Selector::isValid()` as `@internal` (#1037)
 - Mark parsing-related methods of most CSS elements as `@internal` (#908)
diff --git a/src/OutputFormat.php b/src/OutputFormat.php
index 47242968b..b65986bb0 100644
--- a/src/OutputFormat.php
+++ b/src/OutputFormat.php
@@ -751,11 +751,15 @@ public function beLenient(): void
         $this->bIgnoreExceptions = true;
     }
 
+    /**
+     * @internal since 8.8.0
+     */
     public function getFormatter(): OutputFormatter
     {
         if ($this->outputFormatter === null) {
             $this->outputFormatter = new OutputFormatter($this);
         }
+
         return $this->outputFormatter;
     }
 
diff --git a/src/OutputFormatter.php b/src/OutputFormatter.php
index 7b61b0ab6..fb122fe7f 100644
--- a/src/OutputFormatter.php
+++ b/src/OutputFormatter.php
@@ -7,6 +7,9 @@
 use Sabberworm\CSS\Comment\Commentable;
 use Sabberworm\CSS\Parsing\OutputException;
 
+/**
+ * @internal since 8.8.0
+ */
 class OutputFormatter
 {
     /**