diff --git a/wp-includes/post.php b/wp-includes/post.php
index 3922a478b6..7312d1db65 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -1042,7 +1042,8 @@ function register_post_type( $post_type, $args = array() ) {
 	if ( false !== $args->query_var && !empty($wp) ) {
 		if ( true === $args->query_var )
 			$args->query_var = $post_type;
-		$args->query_var = sanitize_title_with_dashes($args->query_var);
+		else
+			$args->query_var = sanitize_title_with_dashes($args->query_var);
 		$wp->add_query_var($args->query_var);
 	}
 
diff --git a/wp-includes/taxonomy.php b/wp-includes/taxonomy.php
index b34fb3f169..04314b4ec7 100644
--- a/wp-includes/taxonomy.php
+++ b/wp-includes/taxonomy.php
@@ -331,7 +331,8 @@ function register_taxonomy( $taxonomy, $object_type, $args = array() ) {
 	if ( false !== $args['query_var'] && !empty($wp) ) {
 		if ( true === $args['query_var'] )
 			$args['query_var'] = $taxonomy;
-		$args['query_var'] = sanitize_title_with_dashes($args['query_var']);
+		else
+			$args['query_var'] = sanitize_title_with_dashes($args['query_var']);
 		$wp->add_query_var($args['query_var']);
 	}