Index: src/wp-includes/link-template.php
===================================================================
--- src/wp-includes/link-template.php	(revision 25202)
+++ src/wp-includes/link-template.php	(working copy)
@@ -1963,7 +1963,9 @@
  * @return string Site url link with optional path appended.
 */
 function get_site_url( $blog_id = null, $path = '', $scheme = null ) {
-	if ( empty( $blog_id ) || !is_multisite() ) {
+	if ( defined( 'WP_INSTALLING' ) && WP_INSTALLING ) {
+		$url = wp_guess_url();
+	} elseif ( empty( $blog_id ) || !is_multisite() ) {
 		$url = get_option( 'siteurl' );
 	} else {
 		switch_to_blog( $blog_id );