diff --git a/src/ifctester/ifctester/facet.py b/src/ifctester/ifctester/facet.py
index e2639b556c..97c24c59a1 100644
--- a/src/ifctester/ifctester/facet.py
+++ b/src/ifctester/ifctester/facet.py
@@ -719,11 +719,12 @@ class Property(Facet):
                         unit = ifcopenshell.util.unit.get_property_unit(prop_entity, inst.wrapped_data.file)
                         if unit and getattr(unit, "Name", None):
                             # TODO support unnamed derived units
+                            output_prefix = "KILO" if unit.UnitType == "MASSUNIT" else None
                             props[pset_name][prop_entity.Name] = ifcopenshell.util.unit.convert(
                                 prop_entity.NominalValue.wrappedValue,
                                 getattr(unit, "Prefix", None),
                                 unit.Name,
-                                None,
+                                output_prefix,
                                 ifcopenshell.util.unit.si_type_names[unit.UnitType],
                             )
                     elif prop_entity.is_a("IfcPhysicalSimpleQuantity"):
diff --git a/src/ifctester/test/test_facet.py b/src/ifctester/test/test_facet.py
index 7bdb85bc01..10d94b2f03 100644
--- a/src/ifctester/test/test_facet.py
+++ b/src/ifctester/test/test_facet.py
@@ -1290,6 +1290,27 @@ class TestProperty:
         run("Properties can be overriden by an occurrence 1/2", facet=facet, inst=wall, expected=True)
         run("Properties can be overriden by an occurrence 2/2", facet=facet, inst=wall_type, expected=False)
 
+        ifc = self.setup_ifc()
+        element = ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcWall")
+        pset = ifcopenshell.api.pset.add_pset(ifc, product=element, name="Foo_Bar")
+        prop = ifc.create_entity(
+            "IfcPropertySingleValue", Name="Foo", NominalValue=ifc.create_entity("IfcMassMeasure", 6.0)
+        )
+        ifcopenshell.api.pset.edit_pset(ifc, pset=pset, properties={"Foo": prop})
+        restriction = Restriction(options={"minExclusive": 5.0}, base="double")
+        facet = Property(propertySet="Foo_Bar", baseName="Foo", value=restriction, dataType="IfcMassMeasure")
+        run("MASSUNIT uses Kg instead of g", facet=facet, inst=element, expected=True)
+        prop.NominalValue = ifc.create_entity("IfcMassMeasure", 4.0)
+        run("MASSUNIT uses Kg instead of g", facet=facet, inst=element, expected=False)
+
+        # add Gram as Unit to force conversion
+        gram_unit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="MASSUNIT")
+        prop.Unit = gram_unit
+        prop.NominalValue = ifc.create_entity("IfcMassMeasure", 6000.0)
+        run("MASSUNIT uses Kg instead of g", facet=facet, inst=element, expected=True)
+        prop.NominalValue = ifc.create_entity("IfcMassMeasure", 6.0)
+        run("MASSUNIT uses Kg instead of g", facet=facet, inst=element, expected=False)
+
     def setup_ifc(self):
         ifc = ifcopenshell.file()
         ifc.createIfcProject()
@@ -1298,7 +1319,8 @@ class TestProperty:
         areaunit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="AREAUNIT", prefix="MILLI")
         volumeunit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="VOLUMEUNIT", prefix="MILLI")
         timeunit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="TIMEUNIT")
-        ifcopenshell.api.unit.assign_unit(ifc, units=[lengthunit, areaunit, volumeunit, timeunit])
+        mass_unit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="MASSUNIT", prefix="KILO")
+        ifcopenshell.api.unit.assign_unit(ifc, units=[lengthunit, areaunit, volumeunit, timeunit, mass_unit])
         return ifc