diff --git a/network/packetrelay/packet_listener_relay.go b/network/packetrelay/packet_listener_relay.go
index 4c060a39..b760073f 100644
--- a/network/packetrelay/packet_listener_relay.go
+++ b/network/packetrelay/packet_listener_relay.go
@@ -43,7 +43,6 @@ var _ PacketReceiver = (*packetListenerReceiver)(nil)
 // PacketListenerRelay creates a new [PacketRelay] that uses the existing [transport.PacketListener] to
 // create connections to a relay.
 type PacketListenerRelay struct {
-	mu               sync.RWMutex
 	listener         transport.PacketListener
 	writeIdleTimeout time.Duration
 }
@@ -52,9 +51,7 @@ type PacketListenerRelay struct {
 // create connections to a relay.
 // This function is useful if you already have an implementation of [transport.PacketListener] and you want to use it
 // with one of the network stacks (for example, network/lwip2transport) as a UDP traffic handler.
-//
-// Associations use a write-idle timeout that is reset only by [PacketSender.SendPacket], not by
-// incoming packets.
+// The writeIdleTimeout is reset only by [PacketSender.SendPacket], not by incoming packets.
 func NewPacketRelayFromPacketListener(pl transport.PacketListener, writeIdleTimeout time.Duration) (*PacketListenerRelay, error) {
 	if pl == nil {
 		return nil, errors.New("pl must not be nil")
@@ -69,34 +66,17 @@ func NewPacketRelayFromPacketListener(pl transport.PacketListener, writeIdleTime
 	return r, nil
 }
 
-// SetWriteIdleTimeout sets the write-idle timeout for new associations.
-// Existing associations keep the timeout they were created with.
-func (relay *PacketListenerRelay) SetWriteIdleTimeout(timeout time.Duration) error {
-	if timeout <= 0 {
-		return errors.New("timeout must be greater than 0")
-	}
-	relay.mu.Lock()
-	defer relay.mu.Unlock()
-	relay.writeIdleTimeout = timeout
-	return nil
-}
-
 // NewAssociation implements [PacketRelay].NewAssociation. It uses [transport.PacketListener].ListenPacket to create
 // a [net.PacketConn], and returns a [PacketSender] and [PacketReceiver] based on this [net.PacketConn].
 func (relay *PacketListenerRelay) NewAssociation() (PacketSender, PacketReceiver, error) {
-	relay.mu.RLock()
-	listener := relay.listener
-	writeIdleTimeout := relay.writeIdleTimeout
-	relay.mu.RUnlock()
-
-	packetConn, err := listener.ListenPacket(context.Background())
+	packetConn, err := relay.listener.ListenPacket(context.Background())
 	if err != nil {
 		return nil, nil, err
 	}
 
 	association := &packetListenerAssociation{
 		packetConn:       packetConn,
-		writeIdleTimeout: writeIdleTimeout,
+		writeIdleTimeout: relay.writeIdleTimeout,
 	}
 	if err := association.refreshDeadline(); err != nil {
 		_ = association.close()
diff --git a/network/packetrelay/packet_listener_relay_test.go b/network/packetrelay/packet_listener_relay_test.go
index 6e199a2b..14fa46c7 100644
--- a/network/packetrelay/packet_listener_relay_test.go
+++ b/network/packetrelay/packet_listener_relay_test.go
@@ -51,48 +51,56 @@ func TestNewPacketRelayFromPacketListenerRejectsInvalidTimeout(t *testing.T) {
 	require.Nil(t, relay)
 }
 
-func TestPacketListenerRelaySetWriteIdleTimeout(t *testing.T) {
-	conn := &fakePacketConn{}
+func TestPacketListenerRelayReceiveTimeoutClosesAssociation(t *testing.T) {
+	conn := &fakePacketConn{readErr: timeoutErr{}}
 	pl := &fakePacketListener{conn: conn}
-	timeout := 5 * time.Minute
 
 	relay, err := NewPacketRelayFromPacketListener(pl, 30*time.Second)
 	require.NoError(t, err)
-	require.NoError(t, relay.SetWriteIdleTimeout(timeout))
-
-	sender, _, err := relay.NewAssociation()
+	_, receiver, err := relay.NewAssociation()
 	require.NoError(t, err)
-	require.Len(t, conn.deadlines, 1)
-	requireDeadlineNear(t, conn.deadlines[0], timeout)
 
-	err = sender.SendPacket([]byte("hello"), netip.MustParseAddrPort("1.2.3.4:53"))
-	require.NoError(t, err)
-	require.Len(t, conn.deadlines, 2)
-	requireDeadlineNear(t, conn.deadlines[1], timeout)
-	require.Len(t, conn.writes, 1)
+	err = receiver.ReceivePackets(&mockPacketHandler{})
+	require.ErrorAs(t, err, &timeoutErr{})
+	require.True(t, conn.isClosed())
 }
 
-func TestPacketListenerRelaySetWriteIdleTimeoutRejectsInvalidTimeout(t *testing.T) {
-	conn := &fakePacketConn{}
-	pl := &fakePacketListener{conn: conn}
-
-	relay, err := NewPacketRelayFromPacketListener(pl, 30*time.Second)
+func TestPacketListenerRelaySendCloseRace(t *testing.T) {
+	relay, err := NewPacketRelayFromPacketListener(&fakePacketListener{conn: &fakePacketConn{}}, time.Second)
+	require.NoError(t, err)
+	sender, _, err := relay.NewAssociation()
 	require.NoError(t, err)
-	require.Error(t, relay.SetWriteIdleTimeout(0))
-}
 
-func TestPacketListenerRelayReceiveTimeoutClosesAssociation(t *testing.T) {
-	conn := &fakePacketConn{readErr: timeoutErr{}}
-	pl := &fakePacketListener{conn: conn}
+	start := make(chan struct{})
+	var wg sync.WaitGroup
+	for range 10 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			<-start
+			_ = sender.SendPacket([]byte("x"), netip.MustParseAddrPort("1.2.3.4:53"))
+		}()
+	}
+	close(start)
+	_ = sender.Close()
+	wg.Wait()
+}
 
-	relay, err := NewPacketRelayFromPacketListener(pl, 30*time.Second)
+func TestPacketListenerRelayReceiveCloseRace(t *testing.T) {
+	conn := newBlockingPacketConn()
+	relay, err := NewPacketRelayFromPacketListener(&connListener{conn: conn}, time.Second)
 	require.NoError(t, err)
-	_, receiver, err := relay.NewAssociation()
+	sender, receiver, err := relay.NewAssociation()
 	require.NoError(t, err)
 
-	err = receiver.ReceivePackets(&mockPacketHandler{})
-	require.ErrorAs(t, err, &timeoutErr{})
-	require.True(t, conn.isClosed())
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		_ = receiver.ReceivePackets(&mockPacketHandler{})
+	}()
+
+	_ = sender.Close()
+	<-done
 }
 
 func requireDeadlineNear(t *testing.T, deadline time.Time, timeout time.Duration) {
@@ -169,6 +177,36 @@ func (c *fakePacketConn) isClosed() bool {
 	return c.closed
 }
 
+// blockingPacketConn blocks ReadFrom until Close is called, simulating a real UDP conn.
+type blockingPacketConn struct {
+	fakePacketConn
+	once   sync.Once
+	closed chan struct{}
+}
+
+func newBlockingPacketConn() *blockingPacketConn {
+	return &blockingPacketConn{closed: make(chan struct{})}
+}
+
+func (c *blockingPacketConn) ReadFrom(p []byte) (int, net.Addr, error) {
+	<-c.closed
+	return 0, nil, net.ErrClosed
+}
+
+func (c *blockingPacketConn) Close() error {
+	c.once.Do(func() { close(c.closed) })
+	return c.fakePacketConn.Close()
+}
+
+// connListener wraps a net.PacketConn as a transport.PacketListener.
+type connListener struct {
+	conn net.PacketConn
+}
+
+func (l *connListener) ListenPacket(_ context.Context) (net.PacketConn, error) {
+	return l.conn, nil
+}
+
 type timeoutErr struct{}
 
 func (timeoutErr) Error() string {