diff --git src/wp-includes/block-supports/duotone.php src/wp-includes/block-supports/duotone.php
index 95428c9c01..c7905b47c6 100644
--- src/wp-includes/block-supports/duotone.php
+++ src/wp-includes/block-supports/duotone.php
@@ -506,6 +506,7 @@ function wp_register_duotone_support( $block_type ) {
  * @param string $block_content Rendered block content.
  * @param array  $block         Block object.
  * @return string Filtered block content.
+ * @global $is_safari.
  */
 function wp_render_duotone_support( $block_content, $block ) {
 	$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );