diff --git a/strix/runtime/caido_bootstrap.py b/strix/runtime/caido_bootstrap.py
index e96181b22..cf493d1c2 100644
--- a/strix/runtime/caido_bootstrap.py
+++ b/strix/runtime/caido_bootstrap.py
@@ -13,7 +13,6 @@ import asyncio
 import contextlib
 import json
 import logging
-import math
 import time
 from typing import TYPE_CHECKING
 
@@ -53,7 +52,7 @@ async def _login_as_guest(
     while attempts == 0 or time.monotonic() < deadline:
         attempts += 1
         remaining = deadline - time.monotonic()
-        exec_timeout = max(1, min(15, math.ceil(remaining)))
+        exec_timeout = min(15, remaining)
         result = await session.exec(
             "curl",
             "-fsS",
diff --git a/tests/test_caido_bootstrap.py b/tests/test_caido_bootstrap.py
index 5e63e18b3..3837d0db2 100644
--- a/tests/test_caido_bootstrap.py
+++ b/tests/test_caido_bootstrap.py
@@ -102,3 +102,31 @@ async def test_login_as_guest_stops_at_deadline(
 
     assert clock.sleeps == [2.0, 3.0]
     assert [call[1]["timeout"] for call in session.calls] == [5, 3]
+
+
+@pytest.mark.asyncio
+async def test_login_as_guest_caps_final_attempt_to_subsecond_budget(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    clock = _install_clock(monkeypatch)
+
+    class _AdvancingSession(_Session):
+        def __init__(self) -> None:
+            super().__init__([_ExecResult(success=False), _ExecResult(success=False)])
+            self._durations = iter([2.9, 0.1])
+
+        async def exec(self, *args: str, **kwargs: Any) -> _ExecResult:
+            result = await super().exec(*args, **kwargs)
+            clock.now += next(self._durations)
+            return result
+
+    session = _AdvancingSession()
+
+    with pytest.raises(RuntimeError, match=r"2 attempts"):
+        await caido_bootstrap._login_as_guest(
+            cast("BaseSandboxSession", session),
+            container_url="http://127.0.0.1:48080",
+            wait_timeout_s=5,
+        )
+
+    assert [call[1]["timeout"] for call in session.calls] == [5, pytest.approx(0.1)]