Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 19170)
+++ wp-includes/user.php	(working copy)
@@ -736,10 +736,8 @@
 	if ( empty( $user_id ) )
 		$user_id = get_current_user_id();
 
-	if ( empty( $blog_id ) ) {
-		global $wpdb;
-		$blog_id = $wpdb->blogid;
-	}
+	if ( empty( $blog_id ) )
+		$blog_id = get_current_blog_id();
 
 	$blogs = get_blogs_of_user( $user_id );
 	if ( is_array( $blogs ) )