diff --git a/src/ifcopenshell-python/ifcopenshell/util/cost.py b/src/ifcopenshell-python/ifcopenshell/util/cost.py
index 875594f1a5..4354e49e90 100644
--- a/src/ifcopenshell-python/ifcopenshell/util/cost.py
+++ b/src/ifcopenshell-python/ifcopenshell/util/cost.py
@@ -196,9 +196,12 @@ def get_cost_items_for_product(product: ifcopenshell.entity_instance) -> list[if
     :return: A list of IfcCostItem objects representing the cost items related to the product.
     """
     cost_items = []
-    for assignment in product.HasAssignments:
-        if assignment.is_a("IfcRelAssignsToControl") and assignment.RelatingControl.is_a("IfcCostItem"):
-            cost_items.append(assignment.RelatingControl)
+    for assignment in product.HasAssignments or []:
+        if assignment.is_a("IfcRelAssignsToControl"):
+            control = assignment.RelatingControl
+            if control and control.is_a("IfcCostItem"):
+                cost_items.append(control)
+
     return cost_items
 
 
diff --git a/src/ifcopenshell-python/test/util/test_cost.py b/src/ifcopenshell-python/test/util/test_cost.py
new file mode 100644
index 0000000000..516a69edd0
--- /dev/null
+++ b/src/ifcopenshell-python/test/util/test_cost.py
@@ -0,0 +1,52 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2021 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import pytest
+
+import ifcopenshell.api.control
+import ifcopenshell.api.cost
+import test.bootstrap
+import ifcopenshell.api.root
+
+import ifcopenshell.util.cost as subject
+
+class TestGetCostItemForProduct(test.bootstrap.IFC4):
+    def test_run(self):
+        model = self.file
+        element = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        cost_schedule = ifcopenshell.api.cost.add_cost_schedule(model)
+        item1 = ifcopenshell.api.cost.add_cost_item(model, cost_schedule=cost_schedule)
+        ifcopenshell.api.control.assign_control(model, related_objects=[element], relating_control=item1)
+        assert list(subject.get_cost_items_for_product(element)) == [item1]
+
+    def test_remove_cost_item(self):
+        model = self.file
+        element = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        cost_schedule = ifcopenshell.api.cost.add_cost_schedule(model)
+        item1 = ifcopenshell.api.cost.add_cost_item(model, cost_schedule=cost_schedule)
+        ifcopenshell.api.control.assign_control(model, related_objects=[element], relating_control=item1)
+        ifcopenshell.api.cost.remove_cost_item(model, cost_item = item1)
+        assert list(subject.get_cost_items_for_product(element)) == []
+
+    def test_no_assigned_cost_items(self):
+        model = self.file
+        element = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        cost_schedule = ifcopenshell.api.cost.add_cost_schedule(model)
+        item1 = ifcopenshell.api.cost.add_cost_item(model, cost_schedule=cost_schedule)
+        assert list(subject.get_cost_items_for_product(element)) == []
+