[Bro] Question on "already defined (Notice::policy)" error

[James Lay]

Hi All,

I'm dabbling with getting Bro to email, so I've added this to my 
local.bro:

redef Notice::mail_dest = "myemail at address.com";

redef Notice::policy += {
     [$result = Notice::ACTION_EMAIL,
      $pred(n: Notice::Info) =
         { return n$note == PacketFilter::Dropped_Packets; }
     ]
};

but I'm getting:

error in /usr/local/bro/share/bro/base/frameworks/notice/./main.bro, 
line 183 and /usr/local/bro/share/bro/site/local.bro, line 101: already 
defined (Notice::policy)

Is there something I'm missing?  Thank you.

James