diff --git a/wp-includes/feed.php b/wp-includes/feed.php
index 34d8652..ad78b56 100644
--- a/wp-includes/feed.php
+++ b/wp-includes/feed.php
@@ -490,7 +490,7 @@ function self_link() {
        $host = $host['host'];
        echo esc_url(
                'http'
-               . ( (isset($_SERVER['https']) && $_SERVER['https'] == 'on') ? 's' : '' ) . '://'
+               . ( (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on') ? 's' : '' ) . '://'
                . $host
                . stripslashes($_SERVER['REQUEST_URI'])
                );