lib/PublicInbox/Msgmap.pm | 6 +++---
 t/msgmap.t                | 6 +++---

diff --git a/lib/PublicInbox/Msgmap.pm b/lib/PublicInbox/Msgmap.pm
index 3fb3805fe82abea0c23684890d1f33004e6815d5..a49b61e8b7f3636eb28cba61ca052c5000b5720c 100644
--- a/lib/PublicInbox/Msgmap.pm
+++ b/lib/PublicInbox/Msgmap.pm
@@ -82,10 +82,10 @@
 sub mid_insert {
 	my ($self, $mid) = @_;
 	my $dbh = $self->{dbh};
-	use constant MID_INSERT => 'INSERT INTO msgmap (mid) VALUES (?)';
-	my $sth = $self->{mid_insert} ||= $dbh->prepare(MID_INSERT);
+	my $sql = 'INSERT OR IGNORE INTO msgmap (mid) VALUES (?)';
+	my $sth = $self->{mid_insert} ||= $dbh->prepare($sql);
 	$sth->bind_param(1, $mid);
-	$sth->execute;
+	return if $sth->execute == 0;
 	$dbh->last_insert_id(undef, undef, 'msgmap', 'num');
 }
 
diff --git a/t/msgmap.t b/t/msgmap.t
index 5c28e54df7542b7031081e5a37cecfa803a68c05..a5232fab6cbc06b75e0aeb3df541f2d8a43c3285 100644
--- a/t/msgmap.t
+++ b/t/msgmap.t
@@ -27,9 +27,9 @@ 	$num2mid{$n} = $mid;
 }
 
 $@ = undef;
-eval { $d->mid_insert('a@b') };
-ok($@, 'error raised when attempting duplicate message ID');
-
+my $ret = $d->mid_insert('a@b');
+is($ret, undef, 'duplicate mid_insert in undef result');
+is($d->num_for('a@b'), $mid2num{'a@b'}, 'existing number not clobbered');
 
 foreach my $n (keys %num2mid) {
 	is($d->mid_for($n), $num2mid{$n}, "num:$n maps correctly");