diff --git a/config.go b/config.go
index f3e28fc..454ffec 100644
--- a/config.go
+++ b/config.go
@@ -380,6 +380,8 @@ func (uc *UpstreamConfig) isControlD() bool {
 }
 
 func (uc *UpstreamConfig) dohTransport(dnsType uint16) http.RoundTripper {
+	uc.mu.Lock()
+	defer uc.mu.Unlock()
 	switch uc.IPStack {
 	case IpStackBoth, IpStackV4, IpStackV6:
 		return uc.transport
diff --git a/config_quic.go b/config_quic.go
index 8c0fb97..ad695a8 100644
--- a/config_quic.go
+++ b/config_quic.go
@@ -82,6 +82,8 @@ func (uc *UpstreamConfig) setupDOH3TransportWithoutPingUpstream() {
 }
 
 func (uc *UpstreamConfig) doh3Transport(dnsType uint16) http.RoundTripper {
+	uc.mu.Lock()
+	defer uc.mu.Unlock()
 	switch uc.IPStack {
 	case IpStackBoth, IpStackV4, IpStackV6:
 		return uc.http3RoundTripper
diff --git a/doh.go b/doh.go
index e831feb..155361e 100644
--- a/doh.go
+++ b/doh.go
@@ -21,13 +21,9 @@ const (
 )
 
 func newDohResolver(uc *UpstreamConfig) *dohResolver {
-	uc.mu.Lock()
-	transport := uc.transport
-	uc.mu.Unlock()
 	r := &dohResolver{
 		endpoint:          uc.u,
 		isDoH3:            uc.Type == ResolverTypeDOH3,
-		transport:         transport,
 		http3RoundTripper: uc.http3RoundTripper,
 		sendClientInfo:    uc.UpstreamSendClientInfo(),
 		uc:                uc,
@@ -39,7 +35,6 @@ type dohResolver struct {
 	uc                *UpstreamConfig
 	endpoint          *url.URL
 	isDoH3            bool
-	transport         *http.Transport
 	http3RoundTripper http.RoundTripper
 	sendClientInfo    bool
 }