diff --git a/chat/room.go b/chat/room.go
index 9539ec9..a144415 100644
--- a/chat/room.go
+++ b/chat/room.go
@@ -54,18 +54,20 @@ type Room struct {
 	commands  Commands
 	closed    bool
 	closeOnce sync.Once
+	checkName func( *message.User ) error
 
 	Members *set.Set
 }
 
 // NewRoom creates a new room.
-func NewRoom() *Room {
+func NewRoom( checkName func( *message.User ) error ) *Room {
 	broadcast := make(chan message.Message, roomBuffer)
 
 	return &Room{
 		broadcast: broadcast,
 		history:   message.NewHistory(historyLen),
 		commands:  *defaultCommands,
+		checkName: checkName,
 
 		Members: set.New(),
 	}
@@ -176,8 +178,12 @@ func (r *Room) Join(u *message.User) (*Member, error) {
 	if u.ID() == "" {
 		return nil, ErrInvalidName
 	}
+	err := r.checkName(u)
+	if err != nil {
+		return nil, err
+	}
 	member := &Member{User: u}
-	err := r.Members.Add(set.Itemize(u.ID(), member))
+	err = r.Members.Add(set.Itemize(u.ID(), member))
 	if err != nil {
 		return nil, err
 	}
@@ -200,11 +206,15 @@ func (r *Room) Leave(u *message.User) error {
 }
 
 // Rename member with a new identity. This will not call rename on the member.
-func (r *Room) Rename(oldID string, u message.Identifier) error {
+func (r *Room) Rename(oldID string, u *Member) error {
 	if u.ID() == "" {
 		return ErrInvalidName
 	}
-	err := r.Members.Replace(oldID, set.Itemize(u.ID(), u))
+	err := r.checkName(u.User)
+	if err != nil {
+		return err
+	}
+	err = r.Members.Replace(oldID, set.Itemize(u.ID(), u))
 	if err != nil {
 		return err
 	}
diff --git a/host.go b/host.go
index 62276ab..8336715 100644
--- a/host.go
+++ b/host.go
@@ -58,7 +58,30 @@ type Host struct {
 
 // NewHost creates a Host on top of an existing listener.
 func NewHost(listener *sshd.SSHListener, auth *Auth) *Host {
-	room := chat.NewRoom()
+
+	checkName := func(user *message.User) error {
+		id := user.Identifier.(*Identity)
+		publicKey := id.PublicKey()
+		if publicKey == nil {
+			return nil
+		}
+		connectedFingerprint := sshd.Fingerprint(id.PublicKey())
+		var fields []string
+		for _, comments := range []map[string]string{auth.adminComments, auth.allowlistComments} {
+			for fingerprint, comment := range comments {
+				fields = strings.Fields(comment)
+				if len(fields) > 0 {
+					keyname := sanitize.Name(fields[0])
+					if len(fields) > 0 && id.ID() == keyname && connectedFingerprint != fingerprint {
+						return errors.New("This name is registered to a different key")
+					}
+				}
+			}
+		}
+		return nil
+	}
+
+	room := chat.NewRoom(checkName)
 	h := Host{
 		Room:     room,
 		listener: listener,