diff --git a/src/Component/Render/GoogleAnalyticsJavaScriptSnippet.php b/src/Component/Render/GoogleAnalyticsJavaScriptSnippet.php
index 775594f..676d715 100644
--- a/src/Component/Render/GoogleAnalyticsJavaScriptSnippet.php
+++ b/src/Component/Render/GoogleAnalyticsJavaScriptSnippet.php
@@ -36,7 +36,7 @@ class GoogleAnalyticsJavaScriptSnippet implements MarkupInterface {
   /**
    * {@inheritdoc}
    */
-  public function jsonSerialize() {
+  public function jsonSerialize(): mixed {
     return $this->__toString();
   }