diff --git a/strix/config/models.py b/strix/config/models.py
index b84e2aa2..cb24c2db 100644
--- a/strix/config/models.py
+++ b/strix/config/models.py
@@ -446,10 +446,12 @@ async def _with_timeouts(
     first = True
     while True:
         limits: list[tuple[float, float, str]] = []
-        gap = first_event if first else idle
+        # Without a first-event bound, the idle bound covers the first event too.
+        on_first = first and bool(first_event)
+        gap = first_event if on_first else idle
         if gap:
             limits.append(
-                (gap, gap, "stream_first_event_timeout" if first else "stream_idle_timeout")
+                (gap, gap, "stream_first_event_timeout" if on_first else "stream_idle_timeout")
             )
         if total:
             limits.append((max(0.0, deadline - time.monotonic()), total, "stream_total_timeout"))
diff --git a/tests/test_stream_idle_timeout.py b/tests/test_stream_idle_timeout.py
index 8ee47cba..2f247d08 100644
--- a/tests/test_stream_idle_timeout.py
+++ b/tests/test_stream_idle_timeout.py
@@ -161,6 +161,8 @@ async def test_first_event_and_whole_stream_are_bounded() -> None:
 
     with pytest.raises(TimeoutError, match="stream_first_event_timeout"):
         [event async for event in _with_timeouts(_slow_start(), idle=5, first_event=0.2)]
+    with pytest.raises(TimeoutError, match="stream_idle_timeout"):
+        [event async for event in _with_timeouts(_slow_start(), idle=0.2)]
     with pytest.raises(TimeoutError, match="stream_total_timeout"):
         [event async for event in _with_timeouts(_endless(), idle=5, total=0.3)]