lib/PublicInbox/ExtMsg.pm | 2 ++

diff --git a/lib/PublicInbox/ExtMsg.pm b/lib/PublicInbox/ExtMsg.pm
index 243b6bad4ccd9d1e990972d828c5bf05ef3539bb..77537c2cd9f1bd4a8f070e0ada83f515b9f12268 100644
--- a/lib/PublicInbox/ExtMsg.pm
+++ b/lib/PublicInbox/ExtMsg.pm
@@ -95,6 +95,8 @@ 		$url .= $listname;
 		unshift @pfx, { srch => $ctx->{srch}, url => $url };
 		foreach my $pfx (@pfx) {
 			my $srch = delete $pfx->{srch} or next;
+
+			# FIXME we may need a proper prefix trie here...
 			if (my $res = $srch->mid_prefix($mid)) {
 				$n_partial += scalar(@$res);
 				$pfx->{res} = $res;