diff --git a/linkchecker.module b/linkchecker.module
index ce283b2..df04a44 100644
--- a/linkchecker.module
+++ b/linkchecker.module
@@ -1707,6 +1707,7 @@ function _linkchecker_cleanup_links() {
   $linkchecker_block_custom = db_select('linkchecker_block_custom', 'lb')
     ->distinct()
     ->fields('lb', array('lid'));
+  $linkchecker_block_custom->addTag('linkcheckerUnion');
 
   // UNION all linkchecker type tables.
   $subquery2 = db_select($linkchecker_block_custom->union($linkchecker_comment)->union($linkchecker_node), 'q1')