diff --git a/cmd/strelaysrv/main.go b/cmd/strelaysrv/main.go
index fea34ccd4..507b3e6c0 100644
--- a/cmd/strelaysrv/main.go
+++ b/cmd/strelaysrv/main.go
@@ -200,7 +200,7 @@ func main() {
 		go natSvc.Serve(ctx)
 		defer cancel()
 		found := make(chan struct{})
-		mapping.OnChanged(func(_ *nat.Mapping, _, _ []nat.Address) {
+		mapping.OnChanged(func() {
 			select {
 			case found <- struct{}{}:
 			default:
diff --git a/lib/connections/tcp_listen.go b/lib/connections/tcp_listen.go
index 54b833a77..13a071334 100644
--- a/lib/connections/tcp_listen.go
+++ b/lib/connections/tcp_listen.go
@@ -76,7 +76,7 @@ func (t *tcpListener) serve(ctx context.Context) error {
 	defer l.Infof("TCP listener (%v) shutting down", tcaddr)
 
 	mapping := t.natService.NewMapping(nat.TCP, tcaddr.IP, tcaddr.Port)
-	mapping.OnChanged(func(_ *nat.Mapping, _, _ []nat.Address) {
+	mapping.OnChanged(func() {
 		t.notifyAddressesChanged(t)
 	})
 	// Should be called after t.mapping is nil'ed out.
diff --git a/lib/nat/service.go b/lib/nat/service.go
index 4c0269c48..078587961 100644
--- a/lib/nat/service.go
+++ b/lib/nat/service.go
@@ -125,11 +125,15 @@ func (s *Service) process(ctx context.Context) (int, time.Duration) {
 
 	s.mut.RLock()
 	for _, mapping := range s.mappings {
-		if mapping.expires.Before(time.Now()) {
+		mapping.mut.RLock()
+		expires := mapping.expires
+		mapping.mut.RUnlock()
+
+		if expires.Before(time.Now()) {
 			toRenew = append(toRenew, mapping)
 		} else {
 			toUpdate = append(toUpdate, mapping)
-			mappingRenewIn := time.Until(mapping.expires)
+			mappingRenewIn := time.Until(expires)
 			if mappingRenewIn < renewIn {
 				renewIn = mappingRenewIn
 			}
@@ -206,41 +210,36 @@ func (s *Service) RemoveMapping(mapping *Mapping) {
 // Optionally takes renew flag which indicates whether or not we should renew
 // mappings with existing natds
 func (s *Service) updateMapping(ctx context.Context, mapping *Mapping, nats map[string]Device, renew bool) {
-	var added, removed []Address
-
 	renewalTime := time.Duration(s.cfg.Options().NATRenewalM) * time.Minute
+
+	mapping.mut.Lock()
+
 	mapping.expires = time.Now().Add(renewalTime)
+	change := s.verifyExistingLocked(ctx, mapping, nats, renew)
+	add := s.acquireNewLocked(ctx, mapping, nats)
 
-	newAdded, newRemoved := s.verifyExistingMappings(ctx, mapping, nats, renew)
-	added = append(added, newAdded...)
-	removed = append(removed, newRemoved...)
+	mapping.mut.Unlock()
 
-	newAdded, newRemoved = s.acquireNewMappings(ctx, mapping, nats)
-	added = append(added, newAdded...)
-	removed = append(removed, newRemoved...)
-
-	if len(added) > 0 || len(removed) > 0 {
-		mapping.notify(added, removed)
+	if change || add {
+		mapping.notify()
 	}
 }
 
-func (s *Service) verifyExistingMappings(ctx context.Context, mapping *Mapping, nats map[string]Device, renew bool) ([]Address, []Address) {
-	var added, removed []Address
-
+func (s *Service) verifyExistingLocked(ctx context.Context, mapping *Mapping, nats map[string]Device, renew bool) (change bool) {
 	leaseTime := time.Duration(s.cfg.Options().NATLeaseM) * time.Minute
 
-	for id, address := range mapping.addressMap() {
+	for id, address := range mapping.extAddresses {
 		select {
 		case <-ctx.Done():
-			return nil, nil
+			return false
 		default:
 		}
 
 		// Delete addresses for NATDevice's that do not exist anymore
 		nat, ok := nats[id]
 		if !ok {
-			mapping.removeAddress(id)
-			removed = append(removed, address)
+			mapping.removeAddressLocked(id)
+			change = true
 			continue
 		} else if renew {
 			// Only perform renewals on the nat's that have the right local IP
@@ -256,35 +255,32 @@ func (s *Service) verifyExistingMappings(ctx context.Context, mapping *Mapping,
 			addr, err := s.tryNATDevice(ctx, nat, mapping.address.Port, address.Port, leaseTime)
 			if err != nil {
 				l.Debugf("Failed to renew %s -> mapping on %s", mapping, address, id)
-				mapping.removeAddress(id)
-				removed = append(removed, address)
+				mapping.removeAddressLocked(id)
+				change = true
 				continue
 			}
 
 			l.Debugf("Renewed %s -> %s mapping on %s", mapping, address, id)
 
 			if !addr.Equal(address) {
-				mapping.removeAddress(id)
-				mapping.setAddress(id, addr)
-				removed = append(removed, address)
-				added = append(added, address)
+				mapping.removeAddressLocked(id)
+				mapping.setAddressLocked(id, addr)
+				change = true
 			}
 		}
 	}
 
-	return added, removed
+	return change
 }
 
-func (s *Service) acquireNewMappings(ctx context.Context, mapping *Mapping, nats map[string]Device) ([]Address, []Address) {
-	var added, removed []Address
-
+func (s *Service) acquireNewLocked(ctx context.Context, mapping *Mapping, nats map[string]Device) (change bool) {
 	leaseTime := time.Duration(s.cfg.Options().NATLeaseM) * time.Minute
-	addrMap := mapping.addressMap()
+	addrMap := mapping.extAddresses
 
 	for id, nat := range nats {
 		select {
 		case <-ctx.Done():
-			return nil, nil
+			return false
 		default:
 		}
 
@@ -310,11 +306,11 @@ func (s *Service) acquireNewMappings(ctx context.Context, mapping *Mapping, nats
 
 		l.Debugf("Acquired %s -> %s mapping on %s", mapping, addr, id)
 
-		mapping.setAddress(id, addr)
-		added = append(added, addr)
+		mapping.setAddressLocked(id, addr)
+		change = true
 	}
 
-	return added, removed
+	return change
 }
 
 // tryNATDevice tries to acquire a port mapping for the given internal address to
diff --git a/lib/nat/structs.go b/lib/nat/structs.go
index 32dae4a5f..29be5b8d1 100644
--- a/lib/nat/structs.go
+++ b/lib/nat/structs.go
@@ -14,7 +14,7 @@ import (
 	"github.com/syncthing/syncthing/lib/sync"
 )
 
-type MappingChangeSubscriber func(*Mapping, []Address, []Address)
+type MappingChangeSubscriber func()
 
 type Mapping struct {
 	protocol Protocol
@@ -26,55 +26,41 @@ type Mapping struct {
 	mut          sync.RWMutex
 }
 
-func (m *Mapping) setAddress(id string, address Address) {
-	m.mut.Lock()
-	if existing, ok := m.extAddresses[id]; !ok || !existing.Equal(address) {
-		l.Infof("New NAT port mapping: external %s address %s to local address %s.", m.protocol, address, m.address)
-		m.extAddresses[id] = address
-	}
-	m.mut.Unlock()
+func (m *Mapping) setAddressLocked(id string, address Address) {
+	l.Infof("New NAT port mapping: external %s address %s to local address %s.", m.protocol, address, m.address)
+	m.extAddresses[id] = address
 }
 
-func (m *Mapping) removeAddress(id string) {
-	m.mut.Lock()
+func (m *Mapping) removeAddressLocked(id string) {
 	addr, ok := m.extAddresses[id]
 	if ok {
 		l.Infof("Removing NAT port mapping: external %s address %s, NAT %s is no longer available.", m.protocol, addr, id)
 		delete(m.extAddresses, id)
 	}
-	m.mut.Unlock()
 }
 
 func (m *Mapping) clearAddresses() {
 	m.mut.Lock()
-	var removed []Address
+	change := len(m.extAddresses) > 0
 	for id, addr := range m.extAddresses {
 		l.Debugf("Clearing mapping %s: ID: %s Address: %s", m, id, addr)
-		removed = append(removed, addr)
 		delete(m.extAddresses, id)
 	}
 	m.expires = time.Time{}
 	m.mut.Unlock()
-	if len(removed) > 0 {
-		m.notify(nil, removed)
+	if change {
+		m.notify()
 	}
 }
 
-func (m *Mapping) notify(added, removed []Address) {
+func (m *Mapping) notify() {
 	m.mut.RLock()
 	for _, subscriber := range m.subscribers {
-		subscriber(m, added, removed)
+		subscriber()
 	}
 	m.mut.RUnlock()
 }
 
-func (m *Mapping) addressMap() map[string]Address {
-	m.mut.RLock()
-	addrMap := m.extAddresses
-	m.mut.RUnlock()
-	return addrMap
-}
-
 func (m *Mapping) Protocol() Protocol {
 	return m.protocol
 }