diff --git a/dns.go b/dns.go
index 5e94d1c2..9a9b0c07 100644
--- a/dns.go
+++ b/dns.go
@@ -52,6 +52,8 @@ func (d *syncDNSClient) Set(client DNSClient) {
 		return
 	}
 
+	d.Close()
+
 	d.Lock()
 	defer d.Unlock()
 
diff --git a/network.go b/network.go
index d526a91f..3b1b721a 100644
--- a/network.go
+++ b/network.go
@@ -84,6 +84,12 @@ func (m *syncInboundHandlerManager) Close() error {
 }
 
 func (m *syncInboundHandlerManager) Set(manager InboundHandlerManager) {
+	if manager == nil {
+		return
+	}
+
+	m.Close()
+
 	m.Lock()
 	defer m.Unlock()
 
@@ -161,6 +167,11 @@ func (m *syncOutboundHandlerManager) Close() error {
 }
 
 func (m *syncOutboundHandlerManager) Set(manager OutboundHandlerManager) {
+	if manager == nil {
+		return
+	}
+
+	m.Close()
 	m.Lock()
 	defer m.Unlock()
 
diff --git a/policy.go b/policy.go
index 1ac9ac1f..4cb9b397 100644
--- a/policy.go
+++ b/policy.go
@@ -87,6 +87,8 @@ func (m *syncPolicyManager) Set(manager PolicyManager) {
 		return
 	}
 
+	m.Close()
+
 	m.Lock()
 	defer m.Unlock()
 
diff --git a/router.go b/router.go
index d3a8031f..bd1e2d81 100644
--- a/router.go
+++ b/router.go
@@ -54,6 +54,11 @@ func (d *syncDispatcher) Close() error {
 }
 
 func (d *syncDispatcher) Set(disp Dispatcher) {
+	if disp == nil {
+		return
+	}
+
+	d.Close()
 	d.Lock()
 	defer d.Unlock()
 
@@ -108,6 +113,11 @@ func (r *syncRouter) Close() error {
 }
 
 func (r *syncRouter) Set(router Router) {
+	if router == nil {
+		return
+	}
+
+	r.Close()
 	r.Lock()
 	defer r.Unlock()