diff --git a/tests/ui/test_deployment_outcome_controller.py b/tests/ui/test_deployment_outcome_controller.py
index 04d513851..23a8147b0 100644
--- a/tests/ui/test_deployment_outcome_controller.py
+++ b/tests/ui/test_deployment_outcome_controller.py
@@ -901,7 +901,12 @@ async def snapshot(self, namespace: str, name: str) -> RawDeploymentOutcomeSnaps
                 reaped.set()
             raise AssertionError("unreachable")
 
-    controller, ui = _controller(HungReader(), deadline_seconds=0.01)
+    # A frozen clock gives the run its whole deadline however late its worker
+    # starts (#511): with the real one, a runner slower than the deadline
+    # marked it elapsed before the reader was ever called. The deadline is
+    # still enforced by the run's real asyncio timeout, so it must outlast the
+    # read task's start on a coarse Windows timer.
+    controller, ui = _controller(HungReader(), deadline_seconds=0.5, clock=lambda: 0.0)
     observer = controller.scale_observer(
         epoch=4,
         namespace="default",