Index: workflow.install
===================================================================
--- workflow.install	(revision 189)
+++ workflow.install	(working copy)
@@ -75,7 +75,7 @@
   );
   $schema['workflow_node_history'] = array(
     'fields' => array(
-      'hid'     => array('type' => 'serial'),
+      'hid'     => array('type' => 'serial', 'not null' => TRUE),
       'nid'     => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE, 'default' => 0, 'disp-width' => '10'),
       'old_sid' => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE, 'default' => 0, 'disp-width' => '10'),
       'sid'     => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE, 'default' => 0, 'disp-width' => '10'),