diff --git a/ZR.Service/mes/mm/MaterialInputService.cs b/ZR.Service/mes/mm/MaterialInputService.cs
index e5d4ab8d..aa29d158 100644
--- a/ZR.Service/mes/mm/MaterialInputService.cs
+++ b/ZR.Service/mes/mm/MaterialInputService.cs
@@ -134,7 +134,7 @@ namespace ZR.Service.mes.mm
 
                     if (ingredient != null)
                     {
-                        workorder.PreviousNumber = workorder.PreviousNumber - ingredient.Previous_numbered ?? 0;
+                        workorder.PreviousNumber = workorder.PreviousNumber - (ingredient.Previous_numbered ?? 0);
                     }