diff --git a/tariff_fetch/urdb/arcadia/rateutils.py b/tariff_fetch/urdb/arcadia/rateutils.py
index f2371d7..7afe5c2 100644
--- a/tariff_fetch/urdb/arcadia/rateutils.py
+++ b/tariff_fetch/urdb/arcadia/rateutils.py
@@ -26,8 +26,10 @@ def tariff_iter_rates_for_dt(
     scenario: Scenario,
     library: Library,
     dt: datetime,
+    _seen: set[int] | None = None,
 ) -> Iterator[TariffRateExtended]:
     """Yield all rate entries that apply for a scenario at a given datetime."""
+    _seen = _seen or set()
 
     rates = tariff.get("rates", [])
     for rate in rates:
@@ -39,6 +41,10 @@ def tariff_iter_rates_for_dt(
         if not rate_is_applied_to_datetime(rate, dt):
             continue
         if rate["rate_bands"]:
+            rate_id = rate["tariff_rate_id"]
+            if rate_id in _seen:
+                continue
+            _seen.add(rate_id)
             yield rate
         elif rider_id := rate.get("rider_id"):
             try:
@@ -49,7 +55,7 @@ def tariff_iter_rates_for_dt(
                     f"Skipping inaccessible rider {rider_id} attached to rate {rate['tariff_rate_id']} ({rate['rate_name']})",
                 )
                 continue
-            yield from tariff_iter_rates_for_dt(rider_tariff, scenario, library, dt)
+            yield from tariff_iter_rates_for_dt(rider_tariff, scenario, library, dt, _seen)
 
 
 # ================================
diff --git a/tests/test_arcadia_urdb_demand.py b/tests/test_arcadia_urdb_demand.py
index d5394fd..a185bdf 100644
--- a/tests/test_arcadia_urdb_demand.py
+++ b/tests/test_arcadia_urdb_demand.py
@@ -153,8 +153,8 @@ def test_build_schedule_must_be_demand_based():
     tariff: TariffExtended = {
         **KW_TARIFF,
         "rates": [
-            {**RATE, "rate_bands": [{**BAND, "rate_amount": 15.0}]},
-            {**DEMAND_RATE, "rate_bands": [{**BAND, "rate_amount": 10.0}]},
+            {**RATE, "tariff_rate_id": 10000, "rate_bands": [{**BAND, "rate_amount": 15.0}]},
+            {**DEMAND_RATE, "tariff_rate_id": 20000, "rate_bands": [{**BAND, "rate_amount": 10.0}]},
         ],
     }
     scenario = make_stub_scenario(tariff)
@@ -209,12 +209,14 @@ def test_build_demand_schedule_averages_sampled_datetimes():
         "rates": [
             {
                 **RATE,
+                "tariff_rate_id": 10000,
                 "charge_type": "DEMAND_BASED",
                 "quantity_key": "base_kw",
                 "rate_bands": [{**BAND, "rate_amount": 5.0}],
             },
             {
                 **RATE,
+                "tariff_rate_id": 20000,
                 "charge_type": "DEMAND_BASED",
                 "quantity_key": "seasonal_kw",
                 "rate_bands": [{**BAND, "rate_amount": 10.0}],
diff --git a/tests/test_arcadia_urdb_rateutils.py b/tests/test_arcadia_urdb_rateutils.py
index 315b51c..35da961 100644
--- a/tests/test_arcadia_urdb_rateutils.py
+++ b/tests/test_arcadia_urdb_rateutils.py
@@ -10,7 +10,16 @@
 from tariff_fetch.urdb.arcadia.exception import RateConversionError, TariffAccessDenied
 from tariff_fetch.urdb.arcadia.library import LibraryDebugStore, TariffLibrary
 from tariff_fetch.urdb.arcadia.scenario import Scenario
-from tests.arcadia_urdb_fixtures import StubLibrary, make_band, make_consumption_rate, make_percentage_rate, make_rate
+from tests.arcadia_urdb_fixtures import (
+    BAND,
+    RATE,
+    TARIFF,
+    StubLibrary,
+    make_band,
+    make_consumption_rate,
+    make_percentage_rate,
+    make_rate,
+)
 
 
 def test_rate_filter_bands_excludes_non_matching_choice_band():
@@ -272,3 +281,43 @@ def iter_pages(self, **kwargs):
         library.get_tariff(77)
 
     assert calls == [77]
+
+
+def test_tariff_iter_rates_for_dt_deduplicates():
+    duplicated_rate = {
+        **RATE,
+        "tariff_rate_id": 18603035,
+        "rate_name": "Universal Service Charge",
+        "rate_bands": [{**BAND, "tariff_rate_id": 18603035, "rate_amount": 0.32}],
+    }
+    rider_pointer_rate = {
+        **RATE,
+        "tariff_rate_id": 18603036,
+        "rate_name": "Universal Service Charge Rider",
+        "rate_bands": [],
+        "rider_id": 669,
+    }
+    parent_tariff = {**TARIFF, "rates": [duplicated_rate, rider_pointer_rate]}
+    rider_tariff = {**TARIFF, "tariff_id": 669, "master_tariff_id": 669, "rates": [duplicated_rate]}
+    rider_calls: list[int] = []
+
+    def get_tariff(tariff_id: int):
+        rider_calls.append(tariff_id)
+        return rider_tariff
+
+    library = SimpleNamespace(
+        tariffs=SimpleNamespace(get_tariff=get_tariff),
+        record_issue=lambda key, message: None,
+    )
+
+    result = list(
+        ru.tariff_iter_rates_for_dt(
+            parent_tariff,  # type: ignore[arg-type]
+            Scenario(1, 2025, False, {"SUPPLY"}),
+            library,  # type: ignore[arg-type]
+            datetime(2025, 1, 1, 0, 30),
+        )
+    )
+
+    assert result == [duplicated_rate]
+    assert rider_calls == [669]