diff --git a/chord/topology.go b/chord/topology.go
index 128a3e0..29995b3 100644
--- a/chord/topology.go
+++ b/chord/topology.go
@@ -3,11 +3,16 @@ package chord
 import (
 	"errors"
 	"net/netip"
+	"sync"
 )
 
 // Node represents a node's topological relations within a Chord network.
+// It is safe to use the methods of Node concurrently.
 type Node struct {
+	// mu guards the mutable fields of the node.
+	mu sync.Mutex
 	// self is the node's own address.
+	// It is fully immutable; the mutex does not protect it.
 	self Peer
 	// pred is the node's predecessor.
 	// If not valid, the predecessor is not currently known.
@@ -27,11 +32,15 @@ func (n *Node) Self() Peer {
 }
 
 func (n *Node) Successor() Peer {
+	n.mu.Lock()
+	defer n.mu.Unlock()
 	return n.succ[0]
 }
 
 // Neighbors returns the node's predecessor and appends its successor list to s.
 func (n *Node) Neighbors(s []Peer) (Peer, []Peer) {
+	n.mu.Lock()
+	defer n.mu.Unlock()
 	return n.pred, append(s, n.succ...)
 }
 
@@ -43,6 +52,8 @@ func (n *Node) IsLocal(id ID) bool {
 // Closest finds the locally known peer which is the closest predecessor of key.
 func (n *Node) Closest(id ID) Peer {
 	self := n.self.id
+	n.mu.Lock()
+	defer n.mu.Unlock()
 	l := n.fingers
 	for i := len(l) - 1; i >= 0; i-- {
 		f := l[i]