diff --git a/wp-admin/gears-manifest.php b/wp-admin/gears-manifest.php
index 889bc58acb..5621ef5375 100644
--- a/wp-admin/gears-manifest.php
+++ b/wp-admin/gears-manifest.php
@@ -15,6 +15,7 @@ function get_bloginfo() {}
 function is_admin() {return true;}
 function site_url() {}
 function admin_url() {}
+function wp_guess_url() {}
 
 require(ABSPATH . '/wp-includes/script-loader.php');
 require(ABSPATH . '/wp-includes/version.php');