--- AnyEvent-MP/MP/Node.pm	2009/08/05 22:40:51	1.13
+++ AnyEvent-MP/MP/Node.pm	2009/08/08 00:22:16	1.14
@@ -204,7 +204,7 @@
 sub monitor {
    my ($self, $portid, $cb) = @_;
 
-   return $cb->()
+   return $cb->(no_such_port => "cannot monitor nonexistent port")
       unless exists $AnyEvent::MP::Base::PORT{$portid};
 
    $AnyEvent::MP::Base::LMON{$portid}{$cb+0} = $cb;