diff --git a/backend/app/payroll/vouchers/service.py b/backend/app/payroll/vouchers/service.py
index f403e9b..00225f5 100644
--- a/backend/app/payroll/vouchers/service.py
+++ b/backend/app/payroll/vouchers/service.py
@@ -318,14 +318,14 @@ def build_voucher_summary(
         salary_months = []
         if salary_list:
             salary_months = [
-                f"{s.payroll_year:04d}-{s.payroll_month:02d}"
+                f"{s.payroll_year if s.payroll_year else 0:04d}-{s.payroll_month if s.payroll_month else 0:02d}"
                 for s in salary_list
             ]
         
         bonus_months = []
         if bonus_list:
             bonus_months = [
-                f"{b.bonus_year:04d}-{b.bonus_month:02d}"
+                f"{b.bonus_year if b.bonus_year else 0:04d}-{b.bonus_month if b.bonus_month else 0:02d}"
                 for b in bonus_list
             ]
         
@@ -349,8 +349,9 @@ def export_vouchers(request: VoucherExportRequest) -> VoucherExportResponse:
     """账票エクスポート処理（メイン）"""
     try:
         # リクエストログ
-        end_label = f"{request.end_year:04d}-{request.end_month:02d}" if request.end_year else "None"
-        logger.info(f"エクスポート要求: start={request.start_year:04d}-{request.start_month:02d}, "
+        end_label = f"{request.end_year:04d}-{request.end_month:02d}" if request.end_year and request.end_month else "None"
+        start_label = f"{request.start_year:04d}-{request.start_month:02d}" if request.start_year and request.start_month else "None"
+        logger.info(f"エクスポート要求: start={start_label}, "
                     f"end={end_label}, "
                     f"type={request.voucher_type}, employees={request.employee_ids}")