diff --git a/erpnext/manufacturing/doctype/bom/bom.py b/erpnext/manufacturing/doctype/bom/bom.py
index 54fe063fcf0..e33e81d5aaa 100644
--- a/erpnext/manufacturing/doctype/bom/bom.py
+++ b/erpnext/manufacturing/doctype/bom/bom.py
@@ -282,6 +282,7 @@ class BOM(WebsiteGenerator):
 		self.clear_inspection()
 		self.validate_main_item()
 		self.validate_currency()
+		self.set_operation_finished_goods()
 		self.set_materials_based_on_operation_bom()
 		self.set_conversion_rate()
 		self.set_plc_conversion_rate()
@@ -304,8 +305,23 @@ class BOM(WebsiteGenerator):
 		self.set_fg_cost_allocation()
 		self.validate_total_cost_allocation()
 
+<<<<<<< HEAD
 		if self.docstatus == 1:
 			self.validate_raw_materials_of_operation()
+=======
+	def set_operation_finished_goods(self):
+		"""Fill each operation's FG item where it is unambiguous: the final operation produces
+		this BOM's item, an operation with a BOM produces that BOM's item. Runs before
+		set_materials_based_on_operation_bom so derived rows get their materials expanded."""
+		if not self.track_semi_finished_goods:
+			return
+
+		for row in self.operations:
+			if row.is_final_finished_good and not row.finished_good:
+				row.finished_good = self.item
+			elif row.bom_no and not row.finished_good:
+				row.finished_good = frappe.get_cached_value("BOM", row.bom_no, "item")
+>>>>>>> 1e2e87daac (fix: derive operation FG items before material expansion, keep the final one the BOM's item)
 
 	def validate_semi_finished_goods(self):
 		if not self.track_semi_finished_goods or not self.operations:
@@ -313,12 +329,6 @@ class BOM(WebsiteGenerator):
 
 		fg_items = []
 		for row in self.operations:
-			if row.bom_no and not row.finished_good:
-				row.finished_good = frappe.get_cached_value("BOM", row.bom_no, "item")
-
-			if row.is_final_finished_good and not row.finished_good:
-				row.finished_good = self.item
-
 			if not row.finished_good:
 				frappe.throw(
 					_(
@@ -329,6 +339,13 @@ class BOM(WebsiteGenerator):
 			if not row.is_final_finished_good:
 				continue
 
+			if row.finished_good != self.item:
+				frappe.throw(
+					_(
+						"Row #{0}: The operation {1} has 'Is Final Finished Good' checked, so its FG / Semi FG Item must be {2}."
+					).format(row.idx, bold(row.operation), bold(self.item)),
+				)
+
 			fg_items.append(row.finished_good)
 
 		if not fg_items: