diff --git a/src/wp-includes/customize/class-wp-customize-selective-refresh.php b/src/wp-includes/customize/class-wp-customize-selective-refresh.php
index 87113486b2..0b5c446131 100644
--- a/src/wp-includes/customize/class-wp-customize-selective-refresh.php
+++ b/src/wp-includes/customize/class-wp-customize-selective-refresh.php
@@ -49,7 +49,7 @@ final class WP_Customize_Selective_Refresh {
 	 * Keep track of the current partial being rendered.
 	 *
 	 * @since 4.5.0
-	 * @var string
+	 * @var string|null
 	 */
 	protected $current_partial_id;