--- AnyEvent-MP/MP.pm	2009/09/22 09:54:42	1.91
+++ AnyEvent-MP/MP.pm	2009/09/22 14:14:43	1.94
@@ -567,7 +567,7 @@
    $node->monitor ($port, $cb);
 
    defined wantarray
-      and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
+      and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
 }
 
 =item $guard = mon_guard $port, $ref, $ref...