diff --git a/cluster/cluster.go b/cluster/cluster.go
index a12beb95..c282e035 100644
--- a/cluster/cluster.go
+++ b/cluster/cluster.go
@@ -536,7 +536,10 @@ func (p *Peer) peerUpdate(n *memberlist.Node) {
 // AddState adds a new state that will be gossiped. It returns a channel to which
 // broadcast messages for the state can be sent.
 func (p *Peer) AddState(key string, s State, reg prometheus.Registerer) ClusterChannel {
+	p.mtx.Lock()
 	p.states[key] = s
+	p.mtx.Unlock()
+
 	send := func(b []byte) {
 		p.delegate.bcast.QueueBroadcast(simpleBroadcast(b))
 	}
diff --git a/cluster/delegate.go b/cluster/delegate.go
index bcacf83e..394edb0f 100644
--- a/cluster/delegate.go
+++ b/cluster/delegate.go
@@ -157,7 +157,10 @@ func (d *delegate) NotifyMsg(b []byte) {
 		return
 	}
 
+	d.mtx.RLock()
 	s, ok := d.states[p.Key]
+	d.mtx.RUnlock()
+
 	if !ok {
 		return
 	}
@@ -179,6 +182,8 @@ func (d *delegate) GetBroadcasts(overhead, limit int) [][]byte {
 
 // LocalState is called when gossip fetches local state.
 func (d *delegate) LocalState(_ bool) []byte {
+	d.mtx.RLock()
+	defer d.mtx.RUnlock()
 	all := &clusterpb.FullState{
 		Parts: make([]clusterpb.Part, 0, len(d.states)),
 	}