diff --git a/tests/test_energy_cost.py b/tests/test_energy_cost.py
index 9f75d65..6da29e6 100644
--- a/tests/test_energy_cost.py
+++ b/tests/test_energy_cost.py
@@ -1263,6 +1263,9 @@ class TestSummarizePrincipleC:
     def test_future_window_counts_0_days(self, energy_db: Session) -> None:
         """A fully future window (all local dates > today) counts 0 days.
 
+        Pins ``local_now`` to June 25 2026 noon AMS so the 7/1→8/1 window is
+        genuinely in the future regardless of the actual wall-clock date
+        (mirrors the sibling window tests, which all pin ``local_now``).
         Matches table row: 7/1→8/1 (all future) → 0 days.
         """
         eff_utc = _ams_midnight(2026, 6, 1)
@@ -1270,7 +1273,9 @@ class TestSummarizePrincipleC:
 
         start = _ams_midnight(2026, 7, 1)
         end = _ams_midnight(2026, 8, 1)
-        result = self._run_summarize_ams(energy_db, start, end)
+        # Pin local_now to June 25 2026 noon AMS so 7/1→8/1 stays fully future.
+        pinned_now = datetime(2026, 6, 25, 12, 0, 0, tzinfo=_ams())
+        result = self._run_summarize_ams(energy_db, start, end, pinned_now=pinned_now)
 
         assert result["fixed_costs"] == 0.0, (
             f"All-future window must count 0 days; got fixed_costs={result['fixed_costs']}"