diff --git a/src/ifcopenshell-python/ifcopenshell/api/control/assign_control.py b/src/ifcopenshell-python/ifcopenshell/api/control/assign_control.py
index d06224ab40..f8cc67cef6 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/control/assign_control.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/control/assign_control.py
@@ -26,9 +26,9 @@ class Usecase:
             controls = self.settings["relating_control"].Controls[0]
 
         if controls:
-            related_objects = list(controls.RelatedObjects)
-            related_objects.append(self.settings["related_object"])
-            controls.RelatedObjects = related_objects
+            related_objects = set(controls.RelatedObjects)
+            related_objects.add(self.settings["related_object"])
+            controls.RelatedObjects = list(related_objects)
             ifcopenshell.api.run("owner.update_owner_history", self.file, **{"element": controls})
         else:
             controls = self.file.create_entity(
diff --git a/src/ifcopenshell-python/ifcopenshell/api/cost/add_cost_item_quantity.py b/src/ifcopenshell-python/ifcopenshell/api/cost/add_cost_item_quantity.py
index b44282b2b1..dff2d825a0 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/cost/add_cost_item_quantity.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/cost/add_cost_item_quantity.py
@@ -11,6 +11,11 @@ class Usecase:
     def execute(self):
         quantity = self.file.create_entity(self.settings["ifc_class"], Name="Unnamed")
         quantity[3] = 0.0
+        # This is a bold assumption
+        # https://forums.buildingsmart.org/t/how-does-a-cost-item-know-that-it-is-counting-a-controlled-product/3564
+        if self.settings["ifc_class"] == "IfcQuantityCount" and self.settings["cost_item"].Controls:
+            for rel in self.settings["cost_item"].Controls:
+                quantity[3] += len(rel.RelatedObjects)
         quantities = list(self.settings["cost_item"].CostQuantities or [])
         quantities.append(quantity)
         self.settings["cost_item"].CostQuantities = quantities