lib/PublicInbox/SearchIdx.pm  | 6 ++++--
 lib/PublicInbox/V2Writable.pm | 2 +-

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index cc7e7ec922ce812da43c0a6b5a323f7700e663cb..f9207e9464cd1dd3afe89b3b1052635db1682ea5 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -515,13 +515,15 @@ 	$self->remove_message($mid) if defined $mid;
 }
 
 sub index_mm {
-	my ($self, $mime) = @_;
+	my ($self, $mime, $warn_existing) = @_;
 	my $mid = mid_clean(mid_mime($mime));
 	my $mm = $self->{mm};
 	my $num = $mm->mid_insert($mid);
+	return $num if defined $num;
 
+	warn "<$mid> reused\n" if $warn_existing;
 	# fallback to num_for since filters like RubyLang set the number
-	defined $num ? $num : $mm->num_for($mid);
+	$mm->num_for($mid);
 }
 
 sub unindex_mm {
diff --git a/lib/PublicInbox/V2Writable.pm b/lib/PublicInbox/V2Writable.pm
index cf19c7610cb775f1cb09d5c985442046996ce52a..29ed23caaa76fb87fcce3e48caeb4ec7c7f26a23 100644
--- a/lib/PublicInbox/V2Writable.pm
+++ b/lib/PublicInbox/V2Writable.pm
@@ -63,7 +63,7 @@ 	my $oid = $im->{last_object_id};
 	my ($len, $msgref) = @{$im->{last_object}};
 
 	$self->idx_init;
-	my $num = $self->{all}->index_mm($mime);
+	my $num = $self->{all}->index_mm($mime, 1);
 	my $nparts = $self->{partitions};
 	my $part = $num % $nparts;
 	my $idx = $self->idx_part($part);