diff --git a/internal/web/service/client_inbound_apply.go b/internal/web/service/client_inbound_apply.go
index 80105abd9..afce4d888 100644
--- a/internal/web/service/client_inbound_apply.go
+++ b/internal/web/service/client_inbound_apply.go
@@ -807,7 +807,9 @@ func (s *ClientService) UpdateInboundClient(inboundSvc *InboundService, data *mo
 		}
 		// Rename the client record in the same transaction as the settings JSON
 		// so no concurrent SyncInbound can see one renamed without the other.
-		if len(oldEmail) > 0 && !strings.EqualFold(oldEmail, clients[0].Email) {
+		// Byte-level compare (not EqualFold): case-only edits must rename too,
+		// otherwise SyncInbound's case-sensitive lookup creates a duplicate row.
+		if len(oldEmail) > 0 && oldEmail != clients[0].Email {
 			var renameTaken int64
 			if e := tx.Model(&model.ClientRecord{}).Where("email = ?", clients[0].Email).Count(&renameTaken).Error; e != nil {
 				return e
diff --git a/internal/web/service/client_update_rename_test.go b/internal/web/service/client_update_rename_test.go
index d14823cb0..5240c4aeb 100644
--- a/internal/web/service/client_update_rename_test.go
+++ b/internal/web/service/client_update_rename_test.go
@@ -46,6 +46,36 @@ func TestUpdateInboundClientRenameDoesNotDuplicateRecord(t *testing.T) {
 	}
 }
 
+func TestUpdateInboundClientCaseOnlyRenameDoesNotDuplicateRecord(t *testing.T) {
+	setupBulkDB(t)
+	svc := &ClientService{}
+	inboundSvc := &InboundService{}
+
+	source := []model.Client{{Email: "test", ID: "aaaaaaaa-0000-0000-0000-000000000002", SubID: "sub-case", Enable: true}}
+	ib := mkInbound(t, 22002, model.VLESS, clientsSettings(t, source))
+	if err := svc.SyncInbound(nil, ib.Id, source); err != nil {
+		t.Fatalf("seed linkage: %v", err)
+	}
+	origId := lookupClientRecord(t, "test").Id
+
+	updated := source[0]
+	updated.Email = "Test"
+	if _, err := svc.Update(inboundSvc, origId, updated); err != nil {
+		t.Fatalf("Update case-only email: %v", err)
+	}
+
+	if n := countClientRecords(t); n != 1 {
+		t.Fatalf("client records after case-only rename = %d, want 1", n)
+	}
+	rec := lookupClientRecord(t, "Test")
+	if rec.Id != origId {
+		t.Fatalf("record id after case-only rename = %d, want %d", rec.Id, origId)
+	}
+	if rec.Email != "Test" {
+		t.Fatalf("email after case-only rename = %q, want %q", rec.Email, "Test")
+	}
+}
+
 func TestClientUpdateDuplicateSubIDDoesNotRenameEmail(t *testing.T) {
 	setupBulkDB(t)
 	svc := &ClientService{}