diff --git a/Source/NSubstitute.Acceptance.Specs/MultipleThreads.cs b/Source/NSubstitute.Acceptance.Specs/MultipleThreads.cs
index b6f24a5f1..1ccb97c71 100644
--- a/Source/NSubstitute.Acceptance.Specs/MultipleThreads.cs
+++ b/Source/NSubstitute.Acceptance.Specs/MultipleThreads.cs
@@ -139,6 +139,9 @@ public void Returns_multiple_values_is_threadsafe()
             {
                 Assert.Contains(result, results);
             }
+
+            int numberAfterAllReturned = substitute.Number();
+            Assert.That(numberAfterAllReturned, Is.EqualTo(substResults.LastOrDefault()));
         }
 
         public interface IFoo