diff --git a/main.go b/main.go
index a78c185..67d102e 100644
--- a/main.go
+++ b/main.go
@@ -3,10 +3,12 @@ package main
 import (
 	"context"
 	"crypto/tls"
+	"crypto/x509"
 	"encoding/csv"
 	"errors"
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -42,20 +44,22 @@ func arg_fail(msg string) {
 }
 
 type CLIArgs struct {
-	country       string
-	listCountries bool
-	listProxies   bool
-	bindAddress   string
-	verbosity     int
-	timeout       time.Duration
-	showVersion   bool
-	proxy         string
-	apiLogin      string
-	apiPassword   string
-	apiAddress    string
-	bootstrapDNS  string
-	refresh       time.Duration
-	refreshRetry  time.Duration
+	country             string
+	listCountries       bool
+	listProxies         bool
+	bindAddress         string
+	verbosity           int
+	timeout             time.Duration
+	showVersion         bool
+	proxy               string
+	apiLogin            string
+	apiPassword         string
+	apiAddress          string
+	bootstrapDNS        string
+	refresh             time.Duration
+	refreshRetry        time.Duration
+	certChainWorkaround bool
+	caFile              string
 }
 
 func parse_args() CLIArgs {
@@ -80,6 +84,9 @@ func parse_args() CLIArgs {
 			"Examples: https://1.1.1.1/dns-query, quic://dns.adguard.com")
 	flag.DurationVar(&args.refresh, "refresh", 4*time.Hour, "login refresh interval")
 	flag.DurationVar(&args.refreshRetry, "refresh-retry", 5*time.Second, "login refresh retry interval")
+	flag.BoolVar(&args.certChainWorkaround, "certchain-workaround", true,
+		"add bundled cross-signed intermediate cert to certchain to make it check out on old systems")
+	flag.StringVar(&args.caFile, "cafile", "", "use custom CA certificate bundle file")
 	flag.Parse()
 	if args.country == "" {
 		arg_fail("Country can't be empty string.")
@@ -259,7 +266,21 @@ func run() int {
 		return basic_auth_header(seclient.GetProxyCredentials())
 	}
 
-	handlerDialer := NewProxyDialer(endpoint.NetAddr(), fmt.Sprintf("%s0.%s", args.country, PROXY_SUFFIX), auth, dialer)
+	var caPool *x509.CertPool
+	if args.caFile != "" {
+		caPool = x509.NewCertPool()
+		certs, err := ioutil.ReadFile(args.caFile)
+		if err != nil {
+			mainLogger.Error("Can't load CA file: %v", err)
+			return 15
+		}
+		if ok := caPool.AppendCertsFromPEM(certs); !ok {
+			mainLogger.Error("Can't load certificates from CA file")
+			return 15
+		}
+	}
+
+	handlerDialer := NewProxyDialer(endpoint.NetAddr(), fmt.Sprintf("%s0.%s", args.country, PROXY_SUFFIX), auth, args.certChainWorkaround, caPool, dialer)
 	mainLogger.Info("Endpoint: %s", endpoint.NetAddr())
 	mainLogger.Info("Starting proxy server...")
 	handler := NewProxyHandler(handlerDialer, proxyLogger)
diff --git a/upstream.go b/upstream.go
index ff2a0a0..3396564 100644
--- a/upstream.go
+++ b/upstream.go
@@ -6,6 +6,7 @@ import (
 	"context"
 	"crypto/tls"
 	"crypto/x509"
+	"encoding/pem"
 	"errors"
 	"fmt"
 	"io"
@@ -20,10 +21,37 @@ const (
 	PROXY_CONNECT_METHOD       = "CONNECT"
 	PROXY_HOST_HEADER          = "Host"
 	PROXY_AUTHORIZATION_HEADER = "Proxy-Authorization"
+	MISSING_CHAIN_CERT         = `-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
+`
 )
 
 var UpstreamBlockedError = errors.New("blocked by upstream")
 
+var missingLinkDER, _ = pem.Decode([]byte(MISSING_CHAIN_CERT))
+var missingLink, _ = x509.ParseCertificate(missingLinkDER.Bytes)
+
 type Dialer interface {
 	Dial(network, address string) (net.Conn, error)
 }
@@ -34,18 +62,22 @@ type ContextDialer interface {
 }
 
 type ProxyDialer struct {
-	address       string
-	tlsServerName string
-	auth          AuthProvider
-	next          ContextDialer
+	address                string
+	tlsServerName          string
+	auth                   AuthProvider
+	next                   ContextDialer
+	intermediateWorkaround bool
+	caPool                 *x509.CertPool
 }
 
-func NewProxyDialer(address, tlsServerName string, auth AuthProvider, nextDialer ContextDialer) *ProxyDialer {
+func NewProxyDialer(address, tlsServerName string, auth AuthProvider, intermediateWorkaround bool, caPool *x509.CertPool, nextDialer ContextDialer) *ProxyDialer {
 	return &ProxyDialer{
-		address:       address,
-		tlsServerName: tlsServerName,
-		auth:          auth,
-		next:          nextDialer,
+		address:                address,
+		tlsServerName:          tlsServerName,
+		auth:                   auth,
+		next:                   nextDialer,
+		intermediateWorkaround: intermediateWorkaround,
+		caPool:                 caPool,
 	}
 }
 
@@ -79,7 +111,7 @@ func ProxyDialerFromURL(u *url.URL, next ContextDialer) (*ProxyDialer, error) {
 			return authHeader
 		}
 	}
-	return NewProxyDialer(address, tlsServerName, auth, next), nil
+	return NewProxyDialer(address, tlsServerName, auth, false, nil, next), nil
 }
 
 func (d *ProxyDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
@@ -105,9 +137,18 @@ func (d *ProxyDialer) DialContext(ctx context.Context, network, address string)
 				opts := x509.VerifyOptions{
 					DNSName:       d.tlsServerName,
 					Intermediates: x509.NewCertPool(),
+					Roots:         d.caPool,
 				}
+				waRequired := false
 				for _, cert := range cs.PeerCertificates[1:] {
 					opts.Intermediates.AddCert(cert)
+					if d.intermediateWorkaround && !waRequired &&
+						bytes.Compare(cert.AuthorityKeyId, missingLink.SubjectKeyId) == 0 {
+						waRequired = true
+					}
+				}
+				if waRequired {
+					opts.Intermediates.AddCert(missingLink)
 				}
 				_, err := cs.PeerCertificates[0].Verify(opts)
 				return err