diff --git a/datatypes/epc/domain/tests/test_from_rdsap_schema.py b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
index a2463eae..3ba24124 100644
--- a/datatypes/epc/domain/tests/test_from_rdsap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
@@ -431,6 +431,15 @@ class TestFromRdSapSchema21_0_1:
 
         assert result.wet_rooms_count == 0
 
+    def test_omitted_open_chimneys_count_defaults_to_zero_not_none(self) -> None:
+        data = load("21_0_1.json")
+        data.pop("open_chimneys_count", None)
+        schema = from_dict(RdSapSchema21_0_1, data)
+
+        result = EpcPropertyDataMapper.from_rdsap_schema_21_0_1(schema)
+
+        assert result.open_chimneys_count == 0
+
     def test_uprn(self, result: EpcPropertyData) -> None:
         assert result.uprn == 12457