diff --git a/src/ifcopenshell-python/ifcopenshell/util/element.py b/src/ifcopenshell-python/ifcopenshell/util/element.py
index cf6c52e37d..dc05059ec4 100644
--- a/src/ifcopenshell-python/ifcopenshell/util/element.py
+++ b/src/ifcopenshell-python/ifcopenshell/util/element.py
@@ -16,12 +16,14 @@
 # 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 functools
 from collections import namedtuple
 from collections.abc import Callable, Generator, Sequence
 from typing import Any, Literal, Optional, Union, overload
 
 import ifcopenshell
 import ifcopenshell.guid
+import ifcopenshell.ifcopenshell_wrapper
 import ifcopenshell.util.element
 import ifcopenshell.util.representation
 
@@ -1590,10 +1592,36 @@ def replace_element(element: ifcopenshell.entity_instance, replacement: ifcopens
         replace_attribute(inverse, element, replacement)
 
 
+@functools.cache
+def _is_set_attribute(schema_identifier: str, ifc_class: str, index: int) -> bool:
+    """Whether attribute `index` of `ifc_class` is declared as an EXPRESS SET.
+
+    SET aggregates may not contain duplicate members, whereas LIST and BAG
+    aggregates may, so only SET-typed attributes are safe to deduplicate.
+    """
+    declaration = ifcopenshell.ifcopenshell_wrapper.schema_by_name(schema_identifier).declaration_by_name(ifc_class)
+    attribute = declaration.attribute_by_index(index)
+    aggregation = attribute.type_of_attribute().as_aggregation_type()
+    return aggregation is not None and aggregation.type_of_aggregation_string() == "set"
+
+
 def replace_attribute(element: ifcopenshell.entity_instance, old: Any, new: Any) -> None:
     for i, attribute_value in enumerate(element):
         if has_element_reference(attribute_value, old):
-            element[i] = element.walk(lambda v: v == old, lambda v: new, attribute_value)
+            new_value = element.walk(lambda v: v == old, lambda v: new, attribute_value)
+            if (
+                isinstance(attribute_value, tuple)
+                and has_element_reference(attribute_value, new)
+                and _is_set_attribute(element.file.schema_identifier, element.is_a(), i)
+            ):
+                seen: set[Any] = set()
+                deduplicated = []
+                for v in new_value:
+                    if v not in seen:
+                        seen.add(v)
+                        deduplicated.append(v)
+                new_value = tuple(deduplicated)
+            element[i] = new_value
 
 
 def has_element_reference(value: Any, element: ifcopenshell.entity_instance) -> bool:
diff --git a/src/ifcopenshell-python/test/util/test_element.py b/src/ifcopenshell-python/test/util/test_element.py
index ffd5789f01..9ec355f7fe 100644
--- a/src/ifcopenshell-python/test/util/test_element.py
+++ b/src/ifcopenshell-python/test/util/test_element.py
@@ -1244,6 +1244,22 @@ class TestReplaceAttributeIFC4(test.bootstrap.IFC4):
         subject.replace_attribute(rel, old, new)
         assert rel.RelatedObjects == (new,)
 
+    def test_replacing_into_a_set_deduplicates_the_survivor(self):
+        old = self.file.createIfcWall()
+        new = self.file.createIfcWall()
+        rel = self.file.createIfcRelAggregates()
+        rel.RelatedObjects = [old, new]
+        subject.replace_attribute(rel, old, new)
+        assert rel.RelatedObjects == (new,)
+
+    def test_replacing_into_a_list_keeps_legitimate_duplicates(self):
+        p1 = self.file.createIfcCartesianPoint((0.0, 0.0, 0.0))
+        p2 = self.file.createIfcCartesianPoint((1.0, 0.0, 0.0))
+        p3 = self.file.createIfcCartesianPoint((2.0, 0.0, 0.0))
+        polyline = self.file.createIfcPolyline([p1, p2, p3, p1])
+        subject.replace_attribute(polyline, p2, p3)
+        assert polyline.Points == (p1, p3, p3, p1)
+
 
 class TestHasElementReferenceIFC4(test.bootstrap.IFC4):
     def test_if_a_element_attribute_references_another_element(self):