new file mode 100644
--- /dev/null
+++ b/ignore_invalid_headers.t
@@ -0,0 +1,171 @@
+#!/usr/bin/perl
+
+# (C) Sergey Kandaurov
+# (C) Nginx, Inc.
+
+# Tests for ignore_invalid_headers, underscores_in_headers directives.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+
+use Socket qw/ CRLF /;
+use MIME::Base64 qw/ encode_base64 decode_base64 /;
+
+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(9)
+	->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;
+
+        ignore_invalid_headers off;
+
+        location / {
+            proxy_pass http://127.0.0.1:8085;
+        }
+
+        location /v {
+            add_header X-Cookie $http_cookie;
+        }
+    }
+
+    server {
+        listen       127.0.0.1:8081;
+        server_name  localhost;
+
+        location / {
+            proxy_pass http://127.0.0.1:8085;
+        }
+    }
+
+    server {
+        listen       127.0.0.1:8082;
+        server_name  localhost;
+
+        underscores_in_headers on;
+
+        location / {
+            proxy_pass http://127.0.0.1:8085;
+        }
+    }
+}
+
+EOF
+
+$t->write_file('index.html', '');
+$t->write_file('v', '');
+$t->run_daemon(\&http_daemon);
+$t->run()->waitforsocket('127.0.0.1:' . port(8085));
+
+###############################################################################
+
+my $us = 'GET / HTTP/1.0' . CRLF
+	. 'x_foo: x-bar' . CRLF . CRLF;
+my $us2 = 'GET / HTTP/1.0' . CRLF
+	. '_foo: x-bar' . CRLF . CRLF;
+my $bad = 'GET / HTTP/1.0' . CRLF
+	. 'x.foo: x-bar' . CRLF . CRLF;
+my $bad2 = 'GET / HTTP/1.0' . CRLF
+	. '.foo: x-bar' . CRLF . CRLF;
+
+# ignore_invalid_headers off;
+
+like(get($us, 8080), qr/x-bar/, 'off - underscore');
+like(get($us2, 8080), qr/x-bar/, 'off - underscore first');
+like(get($bad, 8080), qr/x-bar/, 'off - bad');
+like(get($bad2, 8080), qr/x-bar/, 'off - bad first');
+
+# ignore_invalid_headers off; headers parsing post 8f55cb5c7e79
+
+TODO: {
+local $TODO = 'not yet' unless $t->has_version('1.17.5');
+
+unlike(http('GET /v HTTP/1.0' . CRLF
+	. 'Host: localhost' . CRLF
+	. 'coo: foo' . CRLF
+	. '</kie>: x-bar' . CRLF . CRLF), qr/x-bar/, 'off - several');
+
+}
+
+# ignore_invalid_headers on;
+
+unlike(get($us, 8081), qr/x-bar/, 'on - underscore');
+unlike(get($us2, 8081), qr/x-bar/, 'on - underscore first');
+
+# ignore_invalid_headers on; underscores_in_headers on;
+
+like(get($us, 8082), qr/x-bar/, 'underscores_in_headers');
+like(get($us2, 8082), qr/x-bar/, 'underscores_in_headers - first');
+
+###############################################################################
+
+sub get {
+	my ($msg, $port) = @_;
+
+	my $s = IO::Socket::INET->new('127.0.0.1:' . port($port)) or die;
+	my ($headers) = http($msg, socket => $s) =~ /X-Headers: (\w+)/;
+	decode_base64($headers);
+}
+
+###############################################################################
+
+sub http_daemon {
+	my $once = 1;
+	my $server = IO::Socket::INET->new(
+		Proto => 'tcp',
+		LocalHost => '127.0.0.1:' . port(8085),
+		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 .= $_;
+			last if (/^\x0d?\x0a?$/);
+		}
+
+		$headers = encode_base64($headers, "");
+
+		print $client <<EOF;
+HTTP/1.1 200 OK
+Connection: close
+X-Headers: $headers
+
+EOF
+
+	}
+}
+
+###############################################################################