lib/PublicInbox/Msgmap.pm | 2 +-

diff --git a/lib/PublicInbox/Msgmap.pm b/lib/PublicInbox/Msgmap.pm
index d474badef16b06a9bf74b63f80224860598d406c..0035c9e3dc1ad8ff5bad1d3201ab06ecf9105032 100644
--- a/lib/PublicInbox/Msgmap.pm
+++ b/lib/PublicInbox/Msgmap.pm
@@ -130,7 +130,7 @@ INSERT OR IGNORE INTO msgmap (mid) VALUES (?)
 
 	return if $sth->execute($mid) == 0;
 	my $num = $dbh->last_insert_id(undef, undef, 'msgmap', 'num');
-	$self->num_highwater($num) unless !defined($num);
+	$self->num_highwater($num) if defined($num);
 	$num;
 }