Index: wp-includes/capabilities.php
===================================================================
--- wp-includes/capabilities.php	(revision 11902)
+++ wp-includes/capabilities.php	(working copy)
@@ -596,6 +596,7 @@
 		update_usermeta( $this->ID, $this->cap_key, $this->caps );
 		$this->get_role_caps();
 		$this->update_user_level_from_caps();
+		do_action('set_user_role', $this->ID, $role);
 	}
 
 	/**