diff --git a/src/ifcopenshell-python/ifcopenshell/util/unit.py b/src/ifcopenshell-python/ifcopenshell/util/unit.py
index 8b2ec3c167..5caff307a8 100644
--- a/src/ifcopenshell-python/ifcopenshell/util/unit.py
+++ b/src/ifcopenshell-python/ifcopenshell/util/unit.py
@@ -683,8 +683,14 @@ def is_attr_type(
             return cur_decl
 
     if isinstance(cur_decl, ifcopenshell_wrapper.aggregation_type):
-        res = cur_decl.type_of_element()
-        cur_decl = res.declared_type()
+        # support aggregate of aggregates, as in IfcCartesianPointList3D.CoordList
+        def get_declared_type_from_aggregate(cur_decl):
+            cur_decl = cur_decl.type_of_element()
+            if not isinstance(cur_decl, ifcopenshell_wrapper.aggregation_type):
+                return cur_decl.declared_type()
+            return get_declared_type_from_aggregate(cur_decl)
+
+        cur_decl = get_declared_type_from_aggregate(cur_decl)
         if hasattr(cur_decl, "name") and cur_decl.name() == ifc_unit_type_name:
             return cur_decl
         while hasattr(cur_decl, "declared_type") is True:
@@ -733,14 +739,16 @@ def convert_file_length_units(ifc_file: ifcopenshell.file, target_units: str) ->
     old_length = [u for u in unit_assignment.Units if getattr(u, "UnitType", None) == "LENGTHUNIT"][0]
     new_length = ifcopenshell.api.run("unit.add_si_unit", file_patched, unit_type="LENGTHUNIT", prefix=prefix)
 
+    # support tuple of tuples, as in IfcCartesianPointList3D.CoordList
+    def convert_value(value):
+        if not isinstance(value, tuple):
+            return convert_unit(value, old_length, new_length)
+        return tuple(convert_value(v) for v in value)
+
     # Traverse all elements and their nested attributes in the file and convert them
     for element, attr, val in iter_element_and_attributes_per_type(file_patched, "IfcLengthMeasure"):
-        if isinstance(val, tuple):
-            new_value = [convert_unit(v, old_length, new_length) for v in val]
-            setattr(element, attr.name(), tuple(new_value))
-        else:
-            new_value = convert_unit(val, old_length, new_length)
-            setattr(element, attr.name(), new_value)
+        new_value = convert_value(val)
+        setattr(element, attr.name(), new_value)
 
     file_patched.remove(old_length)
     unit_assignment.Units = tuple([new_length, *unit_assignment.Units])
diff --git a/src/ifcopenshell-python/test/fixtures/units/polygonal-faces.ifc b/src/ifcopenshell-python/test/fixtures/units/polygonal-faces.ifc
new file mode 100644
index 0000000000..acf56d68b8
--- /dev/null
+++ b/src/ifcopenshell-python/test/fixtures/units/polygonal-faces.ifc
@@ -0,0 +1,79 @@
+ISO-10303-21;
+HEADER;
+FILE_DESCRIPTION(('ViewDefinition[DesignTransferView]'),'2;1');
+FILE_NAME('mill.ifc','2024-04-23T16:52:20+05:00',(),(),'IfcOpenShell v0.7.0-f7c03db75','BlenderBIM 0.0.240422-998f9c6','Nobody');
+FILE_SCHEMA(('IFC4'));
+ENDSEC;
+DATA;
+#1=IFCPROJECT('3Q4HLVId9C$OJq2NqKnvVO',$,'My Project',$,$,$,$,(#14,#26),#9);
+#2=IFCSIUNIT(*,.LENGTHUNIT.,.MILLI.,.METRE.);
+#3=IFCSIUNIT(*,.AREAUNIT.,$,.SQUARE_METRE.);
+#4=IFCSIUNIT(*,.VOLUMEUNIT.,$,.CUBIC_METRE.);
+#5=IFCDIMENSIONALEXPONENTS(0,0,0,0,0,0,0);
+#6=IFCSIUNIT(*,.PLANEANGLEUNIT.,$,.RADIAN.);
+#7=IFCMEASUREWITHUNIT(IFCREAL(0.0174532925199433),#6);
+#8=IFCCONVERSIONBASEDUNIT(#5,.PLANEANGLEUNIT.,'degree',#7);
+#9=IFCUNITASSIGNMENT((#4,#2,#8,#3));
+#10=IFCCARTESIANPOINT((0.,0.,0.));
+#11=IFCDIRECTION((0.,0.,1.));
+#12=IFCDIRECTION((1.,0.,0.));
+#13=IFCAXIS2PLACEMENT3D(#10,#11,#12);
+#14=IFCGEOMETRICREPRESENTATIONCONTEXT($,'Model',3,1.E-05,#13,$);
+#15=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Body','Model',*,*,*,*,#14,$,.MODEL_VIEW.,$);
+#16=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Axis','Model',*,*,*,*,#14,$,.GRAPH_VIEW.,$);
+#17=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Box','Model',*,*,*,*,#14,$,.MODEL_VIEW.,$);
+#18=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Annotation','Model',*,*,*,*,#14,$,.SECTION_VIEW.,$);
+#19=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Annotation','Model',*,*,*,*,#14,$,.ELEVATION_VIEW.,$);
+#20=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Annotation','Model',*,*,*,*,#14,$,.MODEL_VIEW.,$);
+#21=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Annotation','Model',*,*,*,*,#14,$,.PLAN_VIEW.,$);
+#22=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Profile','Model',*,*,*,*,#14,$,.ELEVATION_VIEW.,$);
+#23=IFCCARTESIANPOINT((0.,0.));
+#24=IFCDIRECTION((1.,0.));
+#25=IFCAXIS2PLACEMENT2D(#23,#24);
+#26=IFCGEOMETRICREPRESENTATIONCONTEXT($,'Plan',2,1.E-05,#25,$);
+#27=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Axis','Plan',*,*,*,*,#26,$,.GRAPH_VIEW.,$);
+#28=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Body','Plan',*,*,*,*,#26,$,.PLAN_VIEW.,$);
+#29=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Annotation','Plan',*,*,*,*,#26,$,.PLAN_VIEW.,$);
+#30=IFCSITE('1T8u08wvPCnhfVRFeG_Je7',$,'My Site',$,$,#53,$,$,$,$,$,$,$,$);
+#36=IFCBUILDING('0AGAIai5z9HOTud5I6CjMh',$,'My Building',$,$,#59,$,$,$,$,$,$);
+#42=IFCBUILDINGSTOREY('2lMUoFnMv5KOSnzZ9_MPZv',$,'My Storey',$,$,#65,$,$,$,$);
+#48=IFCRELAGGREGATES('0cjacslobAjw8I_uTLtTuK',$,$,$,#1,(#30));
+#49=IFCCARTESIANPOINT((0.,0.,0.));
+#50=IFCDIRECTION((0.,0.,1.));
+#51=IFCDIRECTION((1.,0.,0.));
+#52=IFCAXIS2PLACEMENT3D(#49,#50,#51);
+#53=IFCLOCALPLACEMENT($,#52);
+#54=IFCRELAGGREGATES('126VmVXPD0pAP2uJz6QYat',$,$,$,#30,(#36));
+#55=IFCCARTESIANPOINT((0.,0.,0.));
+#56=IFCDIRECTION((0.,0.,1.));
+#57=IFCDIRECTION((1.,0.,0.));
+#58=IFCAXIS2PLACEMENT3D(#55,#56,#57);
+#59=IFCLOCALPLACEMENT(#53,#58);
+#60=IFCRELAGGREGATES('1KLZsOP9zAivCjkiTn31bt',$,$,$,#36,(#42));
+#61=IFCCARTESIANPOINT((0.,0.,0.));
+#62=IFCDIRECTION((0.,0.,1.));
+#63=IFCDIRECTION((1.,0.,0.));
+#64=IFCAXIS2PLACEMENT3D(#61,#62,#63);
+#65=IFCLOCALPLACEMENT(#59,#64);
+#66=IFCACTUATOR('3RT$GBDjj6VhZQ2OYV3P13',$,'Cube',$,$,#95,#84,$,.ELECTRICACTUATOR.);
+#72=IFCINDEXEDPOLYGONALFACE((1,2,4,3));
+#73=IFCINDEXEDPOLYGONALFACE((3,4,8,7));
+#74=IFCINDEXEDPOLYGONALFACE((7,8,6,5));
+#75=IFCINDEXEDPOLYGONALFACE((5,6,2,1));
+#76=IFCINDEXEDPOLYGONALFACE((3,7,5,1));
+#77=IFCINDEXEDPOLYGONALFACE((8,4,2,6));
+#78=IFCCARTESIANPOINTLIST3D(((-999.999938964844,-999.999938964844,-999.999938964844),(-999.999938964844,-999.999938964844,999.999938964844),(-999.999938964844,999.999938964844,-999.999938964844),(-999.999938964844,999.999938964844,999.999938964844),(999.999938964844,-999.999938964844,-999.999938964844),(999.999938964844,-999.999938964844,999.999938964844),(999.999938964844,999.999938964844,-999.999938964844),(999.999938964844,999.999938964844,999.999938964844)));
+#79=IFCPOLYGONALFACESET(#78,.T.,(#72,#73,#74,#75,#76,#77),$);
+#80=IFCSHAPEREPRESENTATION(#15,'Body','Tessellation',(#79));
+#81=IFCCARTESIANPOINT((-1000.,-1000.,-1000.));
+#82=IFCBOUNDINGBOX(#81,2000.,2000.,2000.);
+#83=IFCSHAPEREPRESENTATION(#17,'Box','BoundingBox',(#82));
+#84=IFCPRODUCTDEFINITIONSHAPE($,$,(#83,#80));
+#85=IFCRELCONTAINEDINSPATIALSTRUCTURE('107zrsI95BsfGJXI83megf',$,$,$,(#66),#42);
+#91=IFCCARTESIANPOINT((0.,5000.,0.));
+#92=IFCDIRECTION((0.,0.,1.));
+#93=IFCDIRECTION((1.,0.,0.));
+#94=IFCAXIS2PLACEMENT3D(#91,#92,#93);
+#95=IFCLOCALPLACEMENT(#65,#94);
+ENDSEC;
+END-ISO-10303-21;
diff --git a/src/ifcopenshell-python/test/util/test_unit_conversion.py b/src/ifcopenshell-python/test/util/test_unit_conversion.py
index af84677647..22e750c507 100644
--- a/src/ifcopenshell-python/test/util/test_unit_conversion.py
+++ b/src/ifcopenshell-python/test/util/test_unit_conversion.py
@@ -41,9 +41,10 @@ def test_file_units_length_convert(ifc_file):
         elem_id = element.id()
         original_element = f.by_id(elem_id)
         original_val = getattr(original_element, attr.name())
-        if isinstance(original_val, tuple):
-            # assert element is equal to original element times scale
-            assert val == tuple([v * scale for v in original_val])
-        else:
-            # assert element is equal to original element times scale
-            assert val == original_val * scale
+        def convert_value(value):
+            if not isinstance(value, tuple):
+                return value * scale
+            return tuple(convert_value(v) for v in value)
+
+        # assert element is equal to original element times scale
+        assert val == convert_value(original_val)