diff --git a/internal/clientsdb/db.go b/internal/clientsdb/db.go
index b1fb44f..49bf3fc 100644
--- a/internal/clientsdb/db.go
+++ b/internal/clientsdb/db.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"maps"
 	"net"
 	"os"
 	"sync"
@@ -61,16 +62,18 @@ func (db *DB) Add(clientID, comment string) error {
 	db.mu.Lock()
 	defer db.mu.Unlock()
 
-	db.data.Clients[clientID] = ClientInfo{Comment: comment}
-	return db.save()
+	next := Data{Clients: maps.Clone(db.data.Clients)}
+	next.Clients[clientID] = ClientInfo{Comment: comment}
+	return db.save(next)
 }
 
 func (db *DB) Remove(clientID string) error {
 	db.mu.Lock()
 	defer db.mu.Unlock()
 
-	delete(db.data.Clients, clientID)
-	return db.save()
+	next := Data{Clients: maps.Clone(db.data.Clients)}
+	delete(next.Clients, clientID)
+	return db.save(next)
 }
 
 func (db *DB) List() map[string]ClientInfo {
@@ -126,8 +129,8 @@ func (db *DB) loadIfModified() {
 	}
 }
 
-func (db *DB) save() error {
-	b, err := json.MarshalIndent(db.data, "", "  ")
+func (db *DB) save(next Data) error {
+	b, err := json.MarshalIndent(next, "", "  ")
 	if err != nil {
 		return err
 	}
@@ -138,6 +141,8 @@ func (db *DB) save() error {
 		err = os.Rename(tmpFile, db.path)
 	}
 	if err == nil {
+		// Авторизация меняется только после успешной замены файла.
+		db.data = next
 		stat, _ := os.Stat(db.path)
 		if stat != nil {
 			db.lastModified = stat.ModTime()
diff --git a/internal/clientsdb/db_test.go b/internal/clientsdb/db_test.go
index 45cd67c..adc79db 100644
--- a/internal/clientsdb/db_test.go
+++ b/internal/clientsdb/db_test.go
@@ -2,11 +2,55 @@ package clientsdb
 
 import (
 	"net"
+	"os"
 	"path/filepath"
 	"testing"
 	"time"
 )
 
+func TestFailedSavePreservesAuthorization(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "clients.json")
+	db, err := New(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Add("existing", "original"); err != nil {
+		t.Fatal(err)
+	}
+	// Каталог вместо временного файла воспроизводит отказ записи без прав root.
+	if err := os.Mkdir(path+".tmp", 0o700); err != nil {
+		t.Fatal(err)
+	}
+	operations := []struct {
+		name string
+		run  func() error
+	}{
+		{"add", func() error { return db.Add("new", "new") }},
+		{"update", func() error { return db.Add("existing", "changed") }},
+		{"remove", func() error { return db.Remove("existing") }},
+	}
+	for _, op := range operations {
+		t.Run(op.name, func(t *testing.T) {
+			if err := op.run(); err == nil {
+				t.Fatal("save unexpectedly succeeded")
+			}
+			if !db.IsAuthorized("existing") || db.IsAuthorized("new") {
+				t.Fatal("failed save changed authorization")
+			}
+			if got := db.List(); len(got) != 1 || got["existing"].Comment != "original" {
+				t.Fatalf("failed save changed clients: %+v", got)
+			}
+		})
+	}
+	loaded, err := New(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := loaded.List(); len(got) != 1 || got["existing"].Comment != "original" {
+		t.Fatalf("disk changed: %+v", got)
+	}
+}
+
 func TestClientsDB(t *testing.T) {
 	tmpDir := t.TempDir()
 	dbPath := filepath.Join(tmpDir, "clients.json")