diff --git a/wp-admin/update.php b/wp-admin/update.php
index b89ada27de..4290e58d78 100644
--- a/wp-admin/update.php
+++ b/wp-admin/update.php
@@ -252,6 +252,15 @@ if ( isset($_GET['action']) ) {
 		include(ABSPATH . 'wp-admin/admin-footer.php');
 
 	} else {
-		do_action('update-custom_' . $action);
+		/**
+		 * Fires when a custom plugin or theme update request is received.
+		 *
+		 * The dynamic portion of the hook name, $action, refers to the action
+		 * provided in the request for wp-admin/update.php. Can be used to
+		 * provide custom update functionality for themes and plugins.
+		 *
+		 * @since 2.8.0
+		 */
+		do_action( "update-custom_{$action}" );
 	}
 }