lib/PublicInbox/SearchIdx.pm    | 30 ++++++------------------------
 lib/PublicInbox/SearchThread.pm |  2 +-
 lib/PublicInbox/View.pm         | 19 +++++++++++--------

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 1142ca7a0f4c83a6aa4103edc79d91bd04944e5a..8a529c66c2d60257437c55219f0ad028acff22dc 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -291,17 +291,12 @@ 	my $doc = $smsg->{doc};
 	my $mid = $smsg->mid;
 	my $mime = $smsg->{mime};
 	my $hdr = $mime->header_obj;
-	my $refs = $hdr->header_raw('References');
-	my @refs = defined $refs ? ($refs =~ /<([^>]+)>/g) : ();
-	my $irt = $hdr->header_raw('In-Reply-To');
-	if (defined $irt) {
-		if ($irt eq '') {
-			$irt = undef;
-		} else {
-			$irt = mid_clean($irt);
-			$irt = undef if $mid eq $irt;
-		}
-	}
+
+	# last References should be IRT, but some mail clients do things
+	# out of order, so trust IRT over References iff IRT exists
+	my @refs = ($hdr->header_raw('References'),
+			$hdr->header_raw('In-Reply-To'));
+	@refs = ((join(' ', @refs)) =~ /<([^>]+)>/g);
 
 	my $tid;
 	if (@refs) {
@@ -309,15 +304,6 @@ 		my %uniq = ($mid => 1);
 		my @orig_refs = @refs;
 		@refs = ();
 
-		if (defined $irt) {
-			# to check MAX_MID_SIZE
-			push @orig_refs, $irt;
-
-			# below, we will ensure IRT (if specified)
-			# is the last References
-			$uniq{$irt} = 1;
-		}
-
 		# prevent circular references via References: here:
 		foreach my $ref (@orig_refs) {
 			if (length($ref) > MAX_MID_SIZE) {
@@ -328,10 +314,6 @@ 			$uniq{$ref} = 1;
 			push @refs, $ref;
 		}
 	}
-
-	# last References should be IRT, but some mail clients do things
-	# out of order, so trust IRT over References iff IRT exists
-	push @refs, $irt if defined $irt;
 
 	if (@refs) {
 		$smsg->{references} = '<'.join('> <', @refs).'>';
diff --git a/lib/PublicInbox/SearchThread.pm b/lib/PublicInbox/SearchThread.pm
index 2cd066dbf6a58ef837ca803a64025ae2516d9f46..2966907a9d4b3678a47a1b931b2f2287a17db161 100644
--- a/lib/PublicInbox/SearchThread.pm
+++ b/lib/PublicInbox/SearchThread.pm
@@ -7,7 +7,7 @@ # Our own jwz-style threading class based on Mail::Thread from CPAN.
 # Mail::Thread is unmaintained and unavailable on some distros.
 # We also do not want pruning or subject grouping, since we want
 # to encourage strict threading and hopefully encourage people
-# to use proper In-Reply-To.
+# to use proper In-Reply-To/References.
 #
 # This includes fixes from several open bugs for Mail::Thread
 #
diff --git a/lib/PublicInbox/View.pm b/lib/PublicInbox/View.pm
index 2c37cd424e38026ad48f8b3b52ec87382d5d1b1b..0b1ec75b31fd3f297bfcf85fdea29364ba5ede8a 100644
--- a/lib/PublicInbox/View.pm
+++ b/lib/PublicInbox/View.pm
@@ -92,13 +92,13 @@ }
 
 sub in_reply_to {
 	my ($hdr) = @_;
-	my $irt = $hdr->header_raw('In-Reply-To');
-
-	return mid_clean($irt) if defined $irt && $irt ne '';
-
-	my $refs = $hdr->header_raw('References');
-	if ($refs && $refs =~ /<([^>]+)>\s*\z/s) {
-		return $1;
+	my %mid = map { $_ => 1 } $hdr->header_raw('Message-ID');
+	my @refs = ($hdr->header_raw('References'),
+			$hdr->header_raw('In-Reply-To'));
+	@refs = ((join(' ', @refs)) =~ /<([^>]+)>/g);
+	while (defined(my $irt = pop @refs)) {
+		next if $mid{"<$irt>"};
+		return $irt;
 	}
 	undef;
 }
@@ -201,7 +201,10 @@ 	my ($mid_raw, $irt, $id, $ctx) = @_;
 	my $rv = '';
 	my $mapping = $ctx->{mapping} or return $rv;
 	my $pad = '  ';
-	my ($attr, $node, $idx, $level) = @{$mapping->{$mid_raw}};
+	my $mid_map = $mapping->{$mid_raw};
+	defined $mid_map or
+		return 'public-inbox BUG: '.ascii_html($mid_raw).' not mapped';
+	my ($attr, $node, $idx, $level) = @$mid_map;
 	my $children = $node->{children};
 	my $nr_c = scalar @$children;
 	my $nr_s = 0;