lib/PublicInbox/ExtMsg.pm | 2 +-

diff --git a/lib/PublicInbox/ExtMsg.pm b/lib/PublicInbox/ExtMsg.pm
index ab9591f9fc195810a5cea30de84e1ed2d8e8bd24..4e31ef0f37c178208d1d0b2b9d07d56c8d0f251e 100644
--- a/lib/PublicInbox/ExtMsg.pm
+++ b/lib/PublicInbox/ExtMsg.pm
@@ -46,7 +46,7 @@ 			return;
 		}
 
 		# try to find the URL with Xapian to avoid forking
-		my $doc_id = eval { $s->find_unique_doc_id('mid', $mid) };
+		my $doc_id = eval { $s->find_unique_doc_id('XMID' . $mid) };
 		if ($@) {
 			# xapian not configured properly for this repo
 			push @nox, $other;