=== modified file 'privatemsg/pm_block_user/pm_block_user.install'
--- privatemsg/pm_block_user/pm_block_user.install  2010-01-22 20:47:21 +0000
+++ privatemsg/pm_block_user/pm_block_user.install  2010-02-12 19:03:18 +0000
@@ -27,6 +27,7 @@
         'unsigned'      => TRUE,
       ),
     ),
+    'primary key' => array('author', 'recipient'),
   );
 
   return $schema;
@@ -39,3 +40,9 @@
 function pm_block_user_uninstall() {
   drupal_uninstall_schema('pm_block_user');
 }
+
+function pm_block_user_update_6000() {
+  $ret = array();
+  db_add_primary_key($ret, 'pm_block_user', array('author', 'recipient'));
+  return $ret;
+}