diff --git a/proxy_duplicate_headers.t b/proxy_duplicate_headers.t
new file mode 100644
index 0000000..b4d7e56
--- /dev/null
+++ b/proxy_duplicate_headers.t
@@ -0,0 +1,175 @@
+#!/usr/bin/perl
+
+# (C) Maxim Dounin
+
+# Test for http backend returning response with invalid and duplicate
+# headers.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+use Socket qw/ CRLF /;
+
+BEGIN { use FindBin; chdir($FindBin::Bin); }
+
+use lib 'lib';
+use Test::Nginx;
+
+###############################################################################
+
+select STDERR; $| = 1;
+select STDOUT; $| = 1;
+
+my $t = Test::Nginx->new()->has(qw/http proxy/)->plan(8);
+
+$t->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+daemon off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    server {
+        listen       127.0.0.1:8080;
+        server_name  localhost;
+
+        location / {
+            proxy_pass http://127.0.0.1:8081;
+            proxy_read_timeout 1s;
+        }
+    }
+}
+
+EOF
+
+$t->run_daemon(\&http_daemon);
+$t->run()->waitforsocket('127.0.0.1:' . port(8081));
+
+###############################################################################
+
+like(http_get('/'), qr/200 OK/, 'normal');
+
+TODO: {
+local $TODO = 'not yet' unless $t->has_version('1.23.0');
+
+like(http_get('/invalid-length'), qr/502 Bad/, 'invalid length');
+like(http_get('/duplicate-length'), qr/502 Bad/, 'duplicate length');
+like(http_get('/unknown-transfer-encoding'), qr/502 Bad/,
+	'unknown transfer encoding');
+like(http_get('/duplicate-transfer-encoding'), qr/502 Bad/,
+	'duplicate transfer encoding');
+like(http_get('/length-and-transfer-encoding'), qr/502 Bad/,
+	'length and transfer encoding');
+like(http_get('/transfer-encoding-and-length'), qr/502 Bad/,
+	'transfer encoding and length');
+
+like(http_get('/duplicate-expires'), qr/Expires: foo(?!.*bar)/s,
+	'duplicate expires ignored');
+
+}
+
+###############################################################################
+
+sub http_daemon {
+	my $server = IO::Socket::INET->new(
+		Proto => 'tcp',
+		LocalAddr => '127.0.0.1:' . port(8081),
+		Listen => 5,
+		Reuse => 1
+	)
+		or die "Can't create listening socket: $!\n";
+
+	local $SIG{PIPE} = 'IGNORE';
+
+	while (my $client = $server->accept()) {
+		$client->autoflush(1);
+
+		my $headers = '';
+		my $uri = '';
+
+		while (<$client>) {
+			$headers .= $_;
+			last if (/^\x0d?\x0a?$/);
+		}
+
+		$uri = $1 if $headers =~ /^\S+\s+([^ ]+)\s+HTTP/i;
+
+		if ($uri eq '/') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Content-Length: 0' . CRLF . CRLF;
+
+		} elsif ($uri eq '/invalid-length') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Content-Length: foo' . CRLF . CRLF;
+
+		} elsif ($uri eq '/duplicate-length') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Content-Length: 0' . CRLF .
+				'Content-Length: 0' . CRLF . CRLF;
+
+		} elsif ($uri eq '/unknown-transfer-encoding') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Transfer-Encoding: foo' . CRLF . CRLF;
+
+		} elsif ($uri eq '/duplicate-transfer-encoding') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Transfer-Encoding: chunked' . CRLF .
+				'Transfer-Encoding: chunked' . CRLF . CRLF .
+				'0' . CRLF . CRLF;
+
+		} elsif ($uri eq '/length-and-transfer-encoding') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Content-Length: 0' . CRLF .
+				'Transfer-Encoding: chunked' . CRLF . CRLF .
+				'0' . CRLF . CRLF;
+
+		} elsif ($uri eq '/transfer-encoding-and-length') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Transfer-Encoding: chunked' . CRLF .
+				'Content-Length: 0' . CRLF . CRLF .
+				'0' . CRLF . CRLF;
+
+		} elsif ($uri eq '/duplicate-expires') {
+
+			print $client
+				'HTTP/1.1 200 OK' . CRLF .
+				'Connection: close' . CRLF .
+				'Expires: foo' . CRLF .
+				'Expires: bar' . CRLF . CRLF;
+
+		}
+
+		close $client;
+	}
+}
+
+###############################################################################