diff --git a/go-backend/internal/store/sqlite/repository.go b/go-backend/internal/store/sqlite/repository.go
index 7c14603..9ecf3f2 100644
--- a/go-backend/internal/store/sqlite/repository.go
+++ b/go-backend/internal/store/sqlite/repository.go
@@ -2330,13 +2330,25 @@ func (r *Repository) exportTunnels() ([]TunnelBackup, error) {
 	var tunnels []TunnelBackup
 	for rows.Next() {
 		var t TunnelBackup
+		var protocol sql.NullString
+		var updatedTime sql.NullInt64
 		var inIP sql.NullString
-		if err := rows.Scan(&t.ID, &t.Name, &t.TrafficRatio, &t.Type, &t.Protocol, &t.Flow, &t.CreatedTime, &t.UpdatedTime, &t.Status, &inIP, &t.Inx); err != nil {
+		var inx sql.NullInt64
+		if err := rows.Scan(&t.ID, &t.Name, &t.TrafficRatio, &t.Type, &protocol, &t.Flow, &t.CreatedTime, &updatedTime, &t.Status, &inIP, &inx); err != nil {
 			return nil, err
 		}
+		if protocol.Valid {
+			t.Protocol = protocol.String
+		}
+		if updatedTime.Valid {
+			t.UpdatedTime = updatedTime.Int64
+		}
 		if inIP.Valid {
 			t.InIP = inIP.String
 		}
+		if inx.Valid {
+			t.Inx = int(inx.Int64)
+		}
 		// Export chain tunnels
 		chainTunnels, err := r.exportChainTunnels(t.ID)
 		if err != nil {
@@ -2362,12 +2374,23 @@ func (r *Repository) exportChainTunnels(tunnelID int64) ([]ChainTunnelBackup, er
 	for rows.Next() {
 		var ct ChainTunnelBackup
 		var port sql.NullInt64
-		if err := rows.Scan(&ct.ID, &ct.TunnelID, &ct.ChainType, &ct.NodeID, &port, &ct.Strategy, &ct.Inx, &ct.Protocol); err != nil {
+		var strategy, protocol sql.NullString
+		var inx sql.NullInt64
+		if err := rows.Scan(&ct.ID, &ct.TunnelID, &ct.ChainType, &ct.NodeID, &port, &strategy, &inx, &protocol); err != nil {
 			return nil, err
 		}
 		if port.Valid {
 			ct.Port = int(port.Int64)
 		}
+		if strategy.Valid {
+			ct.Strategy = strategy.String
+		}
+		if inx.Valid {
+			ct.Inx = int(inx.Int64)
+		}
+		if protocol.Valid {
+			ct.Protocol = protocol.String
+		}
 		chainTunnels = append(chainTunnels, ct)
 	}
 	return chainTunnels, rows.Err()
@@ -2386,9 +2409,21 @@ func (r *Repository) exportForwards() ([]ForwardBackup, error) {
 	var forwards []ForwardBackup
 	for rows.Next() {
 		var f ForwardBackup
-		if err := rows.Scan(&f.ID, &f.UserID, &f.UserName, &f.Name, &f.TunnelID, &f.RemoteAddr, &f.Strategy, &f.InFlow, &f.OutFlow, &f.CreatedTime, &f.UpdatedTime, &f.Status, &f.Inx); err != nil {
+		var strategy sql.NullString
+		var updatedTime sql.NullInt64
+		var inx sql.NullInt64
+		if err := rows.Scan(&f.ID, &f.UserID, &f.UserName, &f.Name, &f.TunnelID, &f.RemoteAddr, &strategy, &f.InFlow, &f.OutFlow, &f.CreatedTime, &updatedTime, &f.Status, &inx); err != nil {
 			return nil, err
 		}
+		if strategy.Valid {
+			f.Strategy = strategy.String
+		}
+		if updatedTime.Valid {
+			f.UpdatedTime = updatedTime.Int64
+		}
+		if inx.Valid {
+			f.Inx = int(inx.Int64)
+		}
 		forwards = append(forwards, f)
 	}
 	return forwards, rows.Err()
diff --git a/go-backend/tests/contract/migration_contract_test.go b/go-backend/tests/contract/migration_contract_test.go
index 4bc80a3..7ff2bd9 100644
--- a/go-backend/tests/contract/migration_contract_test.go
+++ b/go-backend/tests/contract/migration_contract_test.go
@@ -310,6 +310,80 @@ func TestBackupExportImportRestoreContracts(t *testing.T) {
 			t.Fatalf("expected restored config value v3, got %+v", cfg)
 		}
 	})
+
+	t.Run("backup export tolerates nullable legacy tunnel chain fields", func(t *testing.T) {
+		now := time.Now().UnixMilli()
+		res, err := repo.DB().Exec(`
+			INSERT INTO tunnel(name, traffic_ratio, type, protocol, flow, created_time, updated_time, status, in_ip, inx)
+			VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+		`, "legacy-null-chain", 1.0, 1, "tls", 1000, now, now, 1, nil, 1)
+		if err != nil {
+			t.Fatalf("seed tunnel for nullable chain export: %v", err)
+		}
+		tunnelID, err := res.LastInsertId()
+		if err != nil {
+			t.Fatalf("read tunnel id for nullable chain export: %v", err)
+		}
+
+		if _, err := repo.DB().Exec(`
+			INSERT INTO chain_tunnel(tunnel_id, chain_type, node_id, port, strategy, inx, protocol)
+			VALUES(?, ?, ?, ?, ?, ?, ?)
+		`, tunnelID, "1", 1, nil, nil, nil, nil); err != nil {
+			t.Fatalf("seed nullable chain_tunnel row: %v", err)
+		}
+
+		req := httptest.NewRequest(http.MethodPost, "/api/v1/backup/export", bytes.NewBufferString(`{"types":["tunnels"]}`))
+		req.Header.Set("Authorization", adminToken)
+		req.Header.Set("Content-Type", "application/json")
+		resp := httptest.NewRecorder()
+		router.ServeHTTP(resp, req)
+
+		if resp.Code != http.StatusOK {
+			t.Fatalf("expected status 200, got %d", resp.Code)
+		}
+
+		var payload struct {
+			Version string `json:"version"`
+			Tunnels []struct {
+				ID           int64 `json:"id"`
+				ChainTunnels []struct {
+					Inx      int    `json:"inx"`
+					Strategy string `json:"strategy"`
+					Protocol string `json:"protocol"`
+				} `json:"chainTunnels"`
+			} `json:"tunnels"`
+		}
+		if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
+			t.Fatalf("decode tunnels backup payload: %v", err)
+		}
+		if strings.TrimSpace(payload.Version) == "" {
+			t.Fatalf("expected backup payload version, got empty")
+		}
+
+		found := false
+		for _, tunnel := range payload.Tunnels {
+			if tunnel.ID != tunnelID {
+				continue
+			}
+			if len(tunnel.ChainTunnels) != 1 {
+				t.Fatalf("expected one chain tunnel for seeded tunnel %d, got %d", tunnelID, len(tunnel.ChainTunnels))
+			}
+			if tunnel.ChainTunnels[0].Inx != 0 {
+				t.Fatalf("expected nullable chain inx to export as 0, got %d", tunnel.ChainTunnels[0].Inx)
+			}
+			if tunnel.ChainTunnels[0].Strategy != "" {
+				t.Fatalf("expected nullable chain strategy to export as empty string, got %q", tunnel.ChainTunnels[0].Strategy)
+			}
+			if tunnel.ChainTunnels[0].Protocol != "" {
+				t.Fatalf("expected nullable chain protocol to export as empty string, got %q", tunnel.ChainTunnels[0].Protocol)
+			}
+			found = true
+			break
+		}
+		if !found {
+			t.Fatalf("expected seeded tunnel %d in backup export", tunnelID)
+		}
+	})
 }
 
 type backupExportPayload struct {