diff --git a/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Scripts/ScriptExecutionSchedulerTests.cs b/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Scripts/ScriptExecutionSchedulerTests.cs
index 27997918..86ad91f0 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Scripts/ScriptExecutionSchedulerTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Scripts/ScriptExecutionSchedulerTests.cs
@@ -60,7 +60,10 @@ public class ScriptExecutionSchedulerTests
 
         await WaitUntilAsync(() => scheduler.BusyThreadCount == 1);
         Assert.Equal(1, scheduler.QueueDepth);          // second task waiting
-        Assert.True(scheduler.OldestBusyAge > TimeSpan.Zero);
+        // A busy thread reports a non-null age. Not asserting a strictly-positive
+        // value: Environment.TickCount64 has ~15 ms granularity, so under load the
+        // busy-timestamp and this read can fall in the same tick (age == Zero).
+        Assert.NotNull(scheduler.OldestBusyAge);
 
         gate.Set();
         await Task.WhenAll(blocking, queued);