Index: wp-includes/ms-settings.php
===================================================================
--- wp-includes/ms-settings.php	(revision 23294)
+++ wp-includes/ms-settings.php	(working copy)
@@ -22,21 +22,23 @@
 
 if ( !isset( $current_site ) || !isset( $current_blog ) ) {
 
-	$domain = addslashes( $_SERVER['HTTP_HOST'] );
+	// We don't know if $_SERVER['HTTP_HOST'] or $_SERVER['SERVER_NAME'] is set
+	$domain = $_SERVER['HTTP_HOST'];
+	if ( ! isset( $domain ) && ! empty( $_SERVER['SERVER_NAME'] ) ) {
+		$domain = $_SERVER['SERVER_NAME'];
+	}
+	$domain = addslashes( $domain );
+	// Handle cases with ":PORT_NR" as suffix
 	if ( false !== strpos( $domain, ':' ) ) {
-		if ( substr( $domain, -3 ) == ':80' ) {
-			$domain = substr( $domain, 0, -3 );
-			$_SERVER['HTTP_HOST'] = substr( $_SERVER['HTTP_HOST'], 0, -3 );
-		} elseif ( substr( $domain, -4 ) == ':443' ) {
-			$domain = substr( $domain, 0, -4 );
-			$_SERVER['HTTP_HOST'] = substr( $_SERVER['HTTP_HOST'], 0, -4 );
-		} else {
+		$domain = parse_url( $domain, PHP_URL_PATH );
+		if ( strstr( $domain, ':' ) ) {
 			wp_load_translations_early();
 			wp_die( __( 'Multisite only works without the port number in the URL.' ) );
 		}
+		$_SERVER['HTTP_HOST'] = $_SERVER['SERVER_NAME'] = $domain;
 	}
+	$domain = rtrim( $domain, '.' );
 
-	$domain = rtrim( $domain, '.' );
 	$cookie_domain = $domain;
 	if ( substr( $cookie_domain, 0, 4 ) == 'www.' )
 		$cookie_domain = substr( $cookie_domain, 4 );