Index: wp-includes/canonical.php
===================================================================
--- wp-includes/canonical.php	(revision 15361)
+++ wp-includes/canonical.php	(working copy)
@@ -156,8 +156,8 @@
 
 			$obj = $wp_query->get_queried_object();
 
-			if ( $term_count <= 1 && !empty($obj->term_id) && ( $tax_url = get_term_link((int)$obj->term_id, $obj->taxonomy) ) && !is_wp_error($tax_url) ) {
-
+			if ( $term_count <= 1 && !empty($obj->term_id) && ( $tax_url = get_term_link((int)$obj->term_id, $obj->taxonomy) )
+					&& !is_wp_error($tax_url) && $redirect['query'] ) {
 				if ( is_category() ) {
 					$redirect['query'] = remove_query_arg( array( 'category_name', 'category', 'cat'), $redirect['query']);
 				} elseif ( is_tag() ) {