diff --git a/src/main/java/com/ffii/fpsms/modules/stock/entity/InventoryLotLineRepository.kt b/src/main/java/com/ffii/fpsms/modules/stock/entity/InventoryLotLineRepository.kt
index 04a65f3..1f800a0 100644
--- a/src/main/java/com/ffii/fpsms/modules/stock/entity/InventoryLotLineRepository.kt
+++ b/src/main/java/com/ffii/fpsms/modules/stock/entity/InventoryLotLineRepository.kt
@@ -182,14 +182,25 @@ interface InventoryLotLineRepository : AbstractRepository<InventoryLotLine, Long
 """)
     fun findExpiredItems(@Param("today") today: LocalDate): List<InventoryLotLine>
 
+    /**
+     * Same business key as transfer merge target lookup; restricted to [status] (e.g. AVAILABLE).
+     * Returns a list — never single-result — so duplicate unavailable rows elsewhere do not cause NonUniqueResultException.
+     */
     @Query("""
     SELECT ill FROM InventoryLotLine ill 
     WHERE ill.inventoryLot.lotNo = :lotNo 
     AND ill.inventoryLot.item.id = :itemId
     AND ill.warehouse.id = :warehouseId
     AND ill.deleted = false
+    AND ill.status = :status
+    ORDER BY ill.id ASC
     """)
-    fun findByLotNoAndItemIdAndWarehouseId(lotNo: String, itemId: Long, warehouseId: Long): InventoryLotLine?
+    fun findAllByLotNoAndItemIdAndWarehouseIdAndStatus(
+        @Param("lotNo") lotNo: String,
+        @Param("itemId") itemId: Long,
+        @Param("warehouseId") warehouseId: Long,
+        @Param("status") status: InventoryLotLineStatus,
+    ): List<InventoryLotLine>
 
     @Query("""
     SELECT ill FROM InventoryLotLine ill 
diff --git a/src/main/java/com/ffii/fpsms/modules/stock/service/StockTransferRecordService.kt b/src/main/java/com/ffii/fpsms/modules/stock/service/StockTransferRecordService.kt
index 99c8a2a..36dd5aa 100644
--- a/src/main/java/com/ffii/fpsms/modules/stock/service/StockTransferRecordService.kt
+++ b/src/main/java/com/ffii/fpsms/modules/stock/service/StockTransferRecordService.kt
@@ -13,6 +13,8 @@ import org.springframework.stereotype.Service
 import org.springframework.transaction.annotation.Transactional
 import com.ffii.fpsms.modules.stock.entity.InventoryLotLineRepository
 import com.ffii.fpsms.modules.stock.entity.enum.InventoryLotLineStatus
+import org.springframework.http.HttpStatus
+import org.springframework.web.server.ResponseStatusException
 
 
 @Service
@@ -110,21 +112,28 @@ open class StockTransferRecordService(
             warehouseId = request.warehouseId
         )
 
-        val existingTargetLotLine = inventoryLotLineRepository.findByLotNoAndItemIdAndWarehouseId(
+        val warehouseId = request.warehouseId
+        val mergeCandidates = inventoryLotLineRepository.findAllByLotNoAndItemIdAndWarehouseIdAndStatus(
             lotNo = lotNo,
             itemId = itemId,
-            warehouseId = request.warehouseId
-        )
-
-        return if (
-            existingTargetLotLine != null &&
-            existingTargetLotLine.status == InventoryLotLineStatus.AVAILABLE &&
-            existingTargetLotLine.id != inventoryLotLine.id
-        ) {
-            stockInLineService.createStockInForExistingInventoryLotLine(stockInRequest, existingTargetLotLine) to
-                TransferStockInMode.MERGED_EXISTING_LOT
-        } else {
-            stockInLineService.createStockIn(stockInRequest) to TransferStockInMode.CREATED_NEW_LOT
+            warehouseId = warehouseId,
+            status = InventoryLotLineStatus.AVAILABLE,
+        ).filter { it.id != inventoryLotLine.id }
+
+        return when {
+            mergeCandidates.isEmpty() ->
+                stockInLineService.createStockIn(stockInRequest) to TransferStockInMode.CREATED_NEW_LOT
+            mergeCandidates.size == 1 ->
+                stockInLineService.createStockInForExistingInventoryLotLine(
+                    stockInRequest,
+                    mergeCandidates.single(),
+                ) to TransferStockInMode.MERGED_EXISTING_LOT
+            else ->
+                throw ResponseStatusException(
+                    HttpStatus.BAD_REQUEST,
+                    "目標倉在同一品項與批號下有多筆可用的庫存批號行，無法自動併批；請檢查資料。" +
+                        " (Multiple AVAILABLE inventory lot lines for same warehouse, item, lotNo.)",
+                )
         }
     }