diff --git a/loopx/quota.py b/loopx/quota.py
index eded708cd4..3a6c6a7684 100644
--- a/loopx/quota.py
+++ b/loopx/quota.py
@@ -399,7 +399,12 @@ def goal_quota_with_spend_ledger(
     current_time = now or datetime.now(timezone.utc).astimezone()
     if current_time.tzinfo is None:
         current_time = current_time.replace(tzinfo=timezone.utc)
-    window_start = current_time - timedelta(hours=int(payload["window_hours"]))
+    try:
+        window_start = current_time - timedelta(hours=int(payload["window_hours"]))
+    except OverflowError:
+        # A window longer than datetime can represent still covers every
+        # representable event. It must not crash the Goal-wide history read.
+        window_start = datetime.min.replace(tzinfo=current_time.tzinfo)
     contributions: list[tuple[str, str, int]] = []
     spend_event_count = 0
     void_event_count = 0
diff --git a/tests/control_plane/test_quota_rolling_window_projection.py b/tests/control_plane/test_quota_rolling_window_projection.py
index 477dce99fb..9e78f55153 100644
--- a/tests/control_plane/test_quota_rolling_window_projection.py
+++ b/tests/control_plane/test_quota_rolling_window_projection.py
@@ -3,6 +3,8 @@
 from datetime import datetime, timezone
 from typing import Any
 
+import pytest
+
 from loopx.quota import goal_quota_with_spend_ledger
 
 
@@ -123,3 +125,20 @@ def test_rolling_counter_isolated_by_exact_goal_instance() -> None:
     assert current["spend_event_count"] == 1
     assert legacy_owner["spent_slots"] == 1
     assert legacy_owner["spend_event_count"] == 1
+
+
+@pytest.mark.parametrize("window_hours", [10**8, 10**12, 1e12])
+def test_unrepresentable_window_covers_all_history_without_crashing(
+    window_hours: float,
+) -> None:
+    goal = _goal()
+    goal["quota"]["window_hours"] = window_hours
+    spent = _spend("2026-01-01T00:00:00+00:00", "turn-1")
+
+    ledger = goal_quota_with_spend_ledger(
+        goal,
+        [spent],
+        now=datetime(2026, 6, 1, tzinfo=timezone.utc),
+    )
+
+    assert ledger["spent_slots"] == 1