diff --git a/datatypes/epc/domain/tests/test_from_sap_schema.py b/datatypes/epc/domain/tests/test_from_sap_schema.py
index ec9981009..957cc4a44 100644
--- a/datatypes/epc/domain/tests/test_from_sap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_sap_schema.py
@@ -870,6 +870,27 @@ class TestFullSapSchema16xRouting:
         assert epc.door_count == 1
         assert epc.dwelling_type == "Detached house"
 
+    def test_full_sap_16_x_electricity_tariff_is_translated_not_passed_through(
+        self,
+    ) -> None:
+        # A full-SAP 16.x cert lodges the SAP `energy_tariff` code space, not the
+        # RdSAP `meter_type` one. Routing it through the full-SAP mapper (via the
+        # assessment_type=SAP gate) must apply `_sap_17_1_meter_type`: tariff 1 =
+        # standard → STANDARD. Were it raw-passed to the RdSAP normaliser, code 1
+        # = "dual" → SEVEN_HOUR (the prime-lead over-rating bug this guards).
+        from domain.sap10_calculator.tables.table_12a import (
+            Tariff,
+            tariff_from_meter_type,
+        )
+
+        data = load("sap_16_0_full.json")  # electricity_tariff = 1 (standard)
+
+        epc = EpcPropertyDataMapper.from_api_response(data)
+
+        assert tariff_from_meter_type(epc.sap_energy_source.meter_type) is (
+            Tariff.STANDARD
+        )
+
     def test_reduced_16_x_cert_unaffected_by_full_sap_routing(self) -> None:
         # Arrange — a reduced 16.2 cert (assessment_type RdSAP) must stay on the
         # RdSAP path, keeping its top-level property_type.