diff --git a/backend/api/v1/modules/a24/fa/fa_item_lines/dto.py b/backend/api/v1/modules/a24/fa/fa_item_lines/dto.py
index bf4f63d4..6b4cdc52 100644
--- a/backend/api/v1/modules/a24/fa/fa_item_lines/dto.py
+++ b/backend/api/v1/modules/a24/fa/fa_item_lines/dto.py
@@ -53,7 +53,7 @@ class FaLineItemCreateDTO(BaseModel):
     is_subitem: Optional[bool] = Field(False, description="Es subpartida")
     contains_subitems: Optional[bool] = Field(False, description="Contiene subpartidas")
     includes_subitems: Optional[bool] = Field(False, description="Incluye subpartidas")
-    subitem_number: Optional[int] = Field(None, description="Número de subpartida")
+    subitem_number: Optional[int] = Field(0, description="Número de subpartida")
 
     # Special flags
     download: Optional[bool] = Field(None, description="Indicador de descarga")