Index: wp-admin/edit-tags.php
===================================================================
--- wp-admin/edit-tags.php	(revision 18731)
+++ wp-admin/edit-tags.php	(working copy)
@@ -8,7 +8,18 @@
 
 /** WordPress Administration Bootstrap */
 require_once('./admin.php');
-$tax = get_taxonomy( $taxnow );
+
+if ( ! isset( $_GET['taxonomy'] ) )
+	$taxonomy = 'post_tag';
+elseif ( in_array( $_GET['taxonomy'], get_taxonomies( array('show_ui' => true ) ) ) )
+	$taxonomy = $_GET['taxonomy'];
+else
+	wp_die( __( 'Invalid taxonomy' ) );
+
+$_GET['taxonomy'] = $taxonomy;
+
+$tax = get_taxonomy( $taxonomy );
+
 if ( !current_user_can( $tax->cap->manage_terms ) )
 	wp_die( __( 'Cheatin’ uh?' ) );