Index: wp-includes/ms-blogs.php
===================================================================
--- wp-includes/ms-blogs.php	(revision 23609)
+++ wp-includes/ms-blogs.php	(working copy)
@@ -48,7 +48,7 @@
 			$blogname = 'www';
 		$url = rtrim( network_home_url(), '/' );
 		if ( !empty( $blogname ) )
-			$url = preg_replace( '|^([^\.]+://)|', '$1' . $blogname . '.', $url );
+			$url = preg_replace( '|^([^\.]+://)|', "\${1}" . $blogname . '.', $url );
 	} else {
 		$url = network_home_url( $blogname );
 	}