Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 16259)
+++ wp-includes/query.php	(working copy)
@@ -1350,7 +1350,7 @@
 
 			if ( !empty( $qv['post_type'] ) && ! is_array( $qv['post_type'] ) ) {
 				$post_type_obj = get_post_type_object( $qv['post_type'] );
-				if ( $post_type_obj->has_archive )
+				if ( ! empty( $post_type_obj->has_archive ) )
 					$this->is_post_type_archive = true;
 			}