diff --git a/frontend/app/(main)/COMPANY_16/sales/customer/page.tsx b/frontend/app/(main)/COMPANY_16/sales/customer/page.tsx
index 514ee0b1..0ba76d35 100644
--- a/frontend/app/(main)/COMPANY_16/sales/customer/page.tsx
+++ b/frontend/app/(main)/COMPANY_16/sales/customer/page.tsx
@@ -2078,15 +2078,18 @@ export default function CustomerManagementPage() {
                             type="checkbox"
                             checked={modalContactForm.is_main === "Y" || modalContactForm.is_main === true}
                             onChange={async (e) => {
-                              if (e.target.checked) {
+                              const checked = e.target.checked;
+                              if (checked) {
                                 const existingMain = modalContacts.find((x) => (x.is_main === "Y" || x.is_main === true) && (x._localId || x.id) !== modalContactEditId);
                                 if (existingMain) {
                                   const ok = await confirm(`현재 메인 담당자는 "${existingMain.contact_name}"입니다. 변경하시겠습니까?`);
                                   if (!ok) return;
                                   setModalContacts((prev) => prev.map((item) => ({ ...item, is_main: "N" })));
                                 }
+                                setModalContactForm((p) => ({ ...p, is_main: "Y" }));
+                              } else {
+                                setModalContactForm((p) => ({ ...p, is_main: "N" }));
                               }
-                              setModalContactForm((p) => ({ ...p, is_main: e.target.checked ? "Y" : "N" }));
                             }}
                             className="rounded"
                           />
@@ -2302,15 +2305,18 @@ export default function CustomerManagementPage() {
                             type="checkbox"
                             checked={modalDeliveryForm.is_default === "Y" || modalDeliveryForm.is_default === true}
                             onChange={async (e) => {
-                              if (e.target.checked) {
+                              const checked = e.target.checked;
+                              if (checked) {
                                 const existingMain = modalDeliveries.find((x) => (x.is_default === "Y" || x.is_default === true) && (x._localId || x.id) !== modalDeliveryEditId);
                                 if (existingMain) {
                                   const ok = await confirm(`현재 메인 납품처는 "${existingMain.destination_name}"입니다. 변경하시겠습니까?`);
                                   if (!ok) return;
                                   setModalDeliveries((prev) => prev.map((item) => ({ ...item, is_default: "N" })));
                                 }
+                                setModalDeliveryForm((p) => ({ ...p, is_default: "Y" }));
+                              } else {
+                                setModalDeliveryForm((p) => ({ ...p, is_default: "N" }));
                               }
-                              setModalDeliveryForm((p) => ({ ...p, is_default: e.target.checked ? "Y" : "N" }));
                             }}
                             className="rounded"
                           />