diff --git a/webform.install b/webform.install
index 9b83935..1740e76 100644
--- a/webform.install
+++ b/webform.install
@@ -1276,7 +1276,7 @@ function webform_update_6321() {
   $ret = array();
   db_add_field($ret, 'webform', 'block', array('type' => 'int', 'size' => 'tiny', 'not null' => TRUE, 'default' => 0));
   db_change_field($ret, 'webform', 'redirect_url', 'redirect_url', array('type' => 'varchar', 'length' => 255, 'default' => '<confirmation>'));
-  update_sql("UPDATE {webform} SET redirect_url = '<confirmation>' WHERE redirect_url = ''");
+  update_sql("UPDATE {webform} SET redirect_url = '<confirmation>' WHERE redirect_url = '' OR redirect_url IS NULL");
   return $ret;
 }