diff --git a/src/equipment/schema.py b/src/equipment/schema.py
index 69dd703..55682b1 100644
--- a/src/equipment/schema.py
+++ b/src/equipment/schema.py
@@ -127,7 +127,7 @@ class EquipmentTop10Pagination(Pagination):
 
 class EquipmentDataMaster(EquipmentBase):
     id: UUID
-    equipment_master: EquipmentMasterBase
+    equipment_master: Optional[EquipmentMasterBase] = Field(None, nullable=True)
     forecasting_target_year: Optional[int] = Field(None, nullable=True)
     minimum_eac_seq: Optional[int] = Field(None, nullable=True)
     minimum_eac_year: Optional[int] = Field(None, nullable=True)