Index: wp-admin/includes/update-core.php
===================================================================
--- wp-admin/includes/update-core.php	(revision 18247)
+++ wp-admin/includes/update-core.php	(working copy)
@@ -344,7 +344,7 @@
 	$roots = array( '/wordpress/', '/wordpress-mu/' );
 	foreach( $roots as $root ) {
 		if ( $wp_filesystem->exists($from . $root . 'wp-settings.php') && $wp_filesystem->exists($from . $root . 'wp-admin/admin.php') &&
-			$wp_filesystem->exists($from . $root . 'wp-includes/functions.php') ) {
+			$wp_filesystem->exists($from . $root . 'wp-includes/version.php') ) {
 			$distro = $root;
 			break;
 		}