diff --git a/src/tck/Reactive.Streams.TCK/TestEnvironment.cs b/src/tck/Reactive.Streams.TCK/TestEnvironment.cs
index 65bcca7..4f9829f 100644
--- a/src/tck/Reactive.Streams.TCK/TestEnvironment.cs
+++ b/src/tck/Reactive.Streams.TCK/TestEnvironment.cs
@@ -861,6 +861,9 @@ public List<T> NextN(long elements, long timeoutMilliseconds, string errorMessag
             {
                 var remainingMilliseconds = (long)(deadline - DateTime.Now).TotalMilliseconds;
 
+                if (remainingMilliseconds < 0)
+                    return _environment.FlopAndFail<List<T>>($"{errorMessage} within {timeoutMilliseconds} ms");
+
                 result.Add(Next(remainingMilliseconds, errorMessage));
                 remaining--;
             }