diff --git a/wp-admin/list-manipulation.php b/wp-admin/list-manipulation.php
index 97f144abbb..63ff21bf6a 100644
--- a/wp-admin/list-manipulation.php
+++ b/wp-admin/list-manipulation.php
@@ -4,7 +4,7 @@ require_once('admin-functions.php');
 require_once('admin-db.php');
 
 get_currentuserinfo();
-if ( !$current_user )
+if ( !is_user_logged_in() )
 	die('-1');
 
 function grab_results() {
diff --git a/wp-includes/classes.php b/wp-includes/classes.php
index 428cee6d25..e97c87ca9c 100644
--- a/wp-includes/classes.php
+++ b/wp-includes/classes.php
@@ -1563,7 +1563,7 @@ class WP {
 	function send_headers() {
 		global $current_user;
 		@header('X-Pingback: '. get_bloginfo('pingback_url'));
-		if ( $current_user )
+		if ( is_user_logged_in() )
 			nocache_headers();
 		if ( !empty($this->query_vars['error']) && '404' == $this->query_vars['error'] ) {
 			status_header( 404 );
diff --git a/wp-includes/pluggable-functions.php b/wp-includes/pluggable-functions.php
index 327ed11dea..444fb029a6 100644
--- a/wp-includes/pluggable-functions.php
+++ b/wp-includes/pluggable-functions.php
@@ -152,6 +152,16 @@ function wp_login($username, $password, $already_md5 = false) {
 }
 endif;
 
+if ( !function_exists('is_user_logged_in') ) :
+function is_user_logged_in() {
+	global $current_user;
+	
+	if ( $current_user->id == 0 )
+		return false;
+	return true;
+}
+endif;
+
 if ( !function_exists('auth_redirect') ) :
 function auth_redirect() {
 	// Checks if a user is logged in, if not redirects them to the login page