lib/PublicInbox/ContentHash.pm |  7 ++++---
 t/v2writable.t                 | 16 ++++++++++++++++

diff --git a/lib/PublicInbox/ContentHash.pm b/lib/PublicInbox/ContentHash.pm
index bacc9cdda12498abbb0ada5d2a2e2faec10190f2..1afbb413a697b99e6ae23b6ef20c1d488526613e 100644
--- a/lib/PublicInbox/ContentHash.pm
+++ b/lib/PublicInbox/ContentHash.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2018-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # Unstable internal API.
@@ -63,8 +63,9 @@ 	# in SearchIdx, so treat them the same for this:
 	# do NOT consider the Message-ID as part of the content_hash
 	# if we got here, we've already got Message-ID reuse
 	my %seen = map { $_ => 1 } @{mids($eml)};
-	foreach my $mid (@{references($eml)}) {
-		$dig->add("ref\0$mid\0") unless $seen{$mid}++;
+	for (grep { !$seen{$_}++ } @{references($eml)}) {
+		utf8::encode($_);
+		$dig->add("ref\0$_\0");
 	}
 
 	# Only use Sender: if From is not present
diff --git a/t/v2writable.t b/t/v2writable.t
index ad946338e0aeb730ba5fa6b6bb6ca41cd61d12dd..0d1022047d49b8853a8e6a9370e3b960c5efde95 100644
--- a/t/v2writable.t
+++ b/t/v2writable.t
@@ -283,6 +283,22 @@ 	is($msgs->[1]->{references}, '<'.('x'x244).'>', 'stored truncated ref');
 	is($msgs->[1]->{mid}, 'y'x244, 'stored truncated mid(2)');
 }
 
+if ('UTF-8 References') {
+	my @w;
+	local $SIG{__WARN__} = sub { push @w, @_ };
+	my $msg = <<EOM;
+From: a\@example.com
+Subject: b
+Message-ID: <horrible\@example>
+References: <\xc4\x80\@example>
+
+EOM
+	ok($im->add(PublicInbox::Eml->new($msg."a\n")), 'UTF-8 References 1');
+	ok($im->add(PublicInbox::Eml->new($msg."b\n")), 'UTF-8 References 2');
+	$im->done;
+	ok(!grep(/Wide character/, @w), 'no wide characters') or xbail(\@w);
+}
+
 my $tmp = {
 	inboxdir => "$inboxdir/non-existent/subdir",
 	name => 'nope',