diff --git a/src/Sextant.Tests/API/ApiApprovalTests.Sextant.net5.0.approved.txt b/src/Sextant.Tests/API/ApiApprovalTests.Sextant.net5.0.approved.txt
index a492fa86..73f6cd13 100644
--- a/src/Sextant.Tests/API/ApiApprovalTests.Sextant.net5.0.approved.txt
+++ b/src/Sextant.Tests/API/ApiApprovalTests.Sextant.net5.0.approved.txt
@@ -153,11 +153,11 @@ namespace Sextant
     public sealed class ViewStackService : Sextant.ViewStackServiceBase
     {
         public ViewStackService(Sextant.IView view) { }
-        public ViewStackService(Sextant.IView view, Sextant.IViewModelFactory? viewModelFactory) { }
+        public ViewStackService(Sextant.IView view, Sextant.IViewModelFactory viewModelFactory) { }
     }
     public abstract class ViewStackServiceBase : Sextant.IViewStackService, Splat.IEnableLogger, System.IDisposable
     {
-        protected ViewStackServiceBase(Sextant.IView view, Sextant.IViewModelFactory? viewModelFactory) { }
+        protected ViewStackServiceBase(Sextant.IView view, Sextant.IViewModelFactory viewModelFactory) { }
         protected Sextant.IViewModelFactory Factory { get; }
         protected Splat.IFullLogger Logger { get; }
         public System.IObservable<System.Collections.Immutable.IImmutableList<Sextant.IViewModel>> ModalStack { get; }
diff --git a/src/Sextant.Tests/API/ApiApprovalTests.Sextant.netcoreapp3.1.approved.txt b/src/Sextant.Tests/API/ApiApprovalTests.Sextant.netcoreapp3.1.approved.txt
index 94739326..54c2dd39 100644
--- a/src/Sextant.Tests/API/ApiApprovalTests.Sextant.netcoreapp3.1.approved.txt
+++ b/src/Sextant.Tests/API/ApiApprovalTests.Sextant.netcoreapp3.1.approved.txt
@@ -153,11 +153,11 @@ namespace Sextant
     public sealed class ViewStackService : Sextant.ViewStackServiceBase
     {
         public ViewStackService(Sextant.IView view) { }
-        public ViewStackService(Sextant.IView view, Sextant.IViewModelFactory? viewModelFactory) { }
+        public ViewStackService(Sextant.IView view, Sextant.IViewModelFactory viewModelFactory) { }
     }
     public abstract class ViewStackServiceBase : Sextant.IViewStackService, Splat.IEnableLogger, System.IDisposable
     {
-        protected ViewStackServiceBase(Sextant.IView view, Sextant.IViewModelFactory? viewModelFactory) { }
+        protected ViewStackServiceBase(Sextant.IView view, Sextant.IViewModelFactory viewModelFactory) { }
         protected Sextant.IViewModelFactory Factory { get; }
         protected Splat.IFullLogger Logger { get; }
         public System.IObservable<System.Collections.Immutable.IImmutableList<Sextant.IViewModel>> ModalStack { get; }
diff --git a/src/Sextant.Tests/Navigation/ParameterViewStackServiceTests.cs b/src/Sextant.Tests/Navigation/ParameterViewStackServiceTests.cs
index 7ab625d9..9d596b1f 100644
--- a/src/Sextant.Tests/Navigation/ParameterViewStackServiceTests.cs
+++ b/src/Sextant.Tests/Navigation/ParameterViewStackServiceTests.cs
@@ -31,16 +31,16 @@ public class TheConstructor
             public TheConstructor() => Locator.GetLocator().UnregisterAll<IViewModelFactory>();
 
             /// <summary>
-            /// Test that the object constructed uses the static instance of ViewModelFactory.
+            /// Test that the object constructed uses a new instance of ViewModelFactory.
             /// </summary>
             [Fact]
-            public void Should_Throw_If_View_Model_Factory_Current_Null()
+            public void Should_Not_Throw_If_View_Model_Factory_Current_Null()
             {
                 // Given, When
                 var result = Record.Exception(() => new ParameterViewStackServiceFixture().WithFactory(null!));
 
                 // Then
-                result.Should().BeOfType<ViewModelFactoryNotFoundException>();
+                result.Should().BeNull();
             }
 
             /// <summary>
diff --git a/src/Sextant.Tests/Navigation/ViewStackServiceTests.cs b/src/Sextant.Tests/Navigation/ViewStackServiceTests.cs
index 07c5d8cb..b14771ad 100644
--- a/src/Sextant.Tests/Navigation/ViewStackServiceTests.cs
+++ b/src/Sextant.Tests/Navigation/ViewStackServiceTests.cs
@@ -33,16 +33,16 @@ public class TheConstructor
             public TheConstructor() => Locator.GetLocator().UnregisterAll<IViewModelFactory>();
 
             /// <summary>
-            /// Test that the object constructed uses the static instance of ViewModelFactory.
+            /// Test that the object constructed uses a new instance of ViewModelFactory.
             /// </summary>
             [Fact]
-            public void Should_Throw_If_View_Model_Factory_Current_Null()
+            public void Should_Not_Throw_If_View_Model_Factory_Current_Null()
             {
                 // Given, When
-                var result = Record.Exception(() => (ViewStackService)new ViewStackServiceFixture().WithFactory(null!));
+                var result = Record.Exception(() => new ParameterViewStackServiceFixture().WithFactory(null!));
 
                 // Then
-                result.Should().BeOfType<ViewModelFactoryNotFoundException>();
+                result.Should().BeNull();
             }
 
             /// <summary>
diff --git a/src/Sextant/Navigation/ParameterViewStackService.cs b/src/Sextant/Navigation/ParameterViewStackService.cs
index 149f8692..c24c430f 100644
--- a/src/Sextant/Navigation/ParameterViewStackService.cs
+++ b/src/Sextant/Navigation/ParameterViewStackService.cs
@@ -17,7 +17,7 @@ public sealed class ParameterViewStackService : ParameterViewStackServiceBase
         /// </summary>
         /// <param name="view">The view.</param>
         public ParameterViewStackService(IView view)
-            : this(view, null!)
+            : this(view, new DefaultViewModelFactory())
         {
         }
 
diff --git a/src/Sextant/Navigation/ViewStackService.cs b/src/Sextant/Navigation/ViewStackService.cs
index 9d6324f6..a17439c6 100644
--- a/src/Sextant/Navigation/ViewStackService.cs
+++ b/src/Sextant/Navigation/ViewStackService.cs
@@ -17,7 +17,7 @@ public sealed class ViewStackService : ViewStackServiceBase
         /// </summary>
         /// <param name="view">The view.</param>
         public ViewStackService(IView view)
-            : this(view, null)
+            : this(view, new DefaultViewModelFactory())
         {
         }
 
@@ -26,7 +26,7 @@ public ViewStackService(IView view)
         /// </summary>
         /// <param name="view">The view.</param>
         /// <param name="viewModelFactory">The view model factory.</param>
-        public ViewStackService(IView view, IViewModelFactory? viewModelFactory)
+        public ViewStackService(IView view, IViewModelFactory viewModelFactory)
             : base(view, viewModelFactory)
         {
         }
diff --git a/src/Sextant/Navigation/ViewStackServiceBase.cs b/src/Sextant/Navigation/ViewStackServiceBase.cs
index bea262de..763e8357 100644
--- a/src/Sextant/Navigation/ViewStackServiceBase.cs
+++ b/src/Sextant/Navigation/ViewStackServiceBase.cs
@@ -28,11 +28,11 @@ public abstract class ViewStackServiceBase : IViewStackService, IDisposable, IEn
         /// </summary>
         /// <param name="view">The view.</param>
         /// <param name="viewModelFactory">The view model factory.</param>
-        protected ViewStackServiceBase(IView view, IViewModelFactory? viewModelFactory)
+        protected ViewStackServiceBase(IView view, IViewModelFactory viewModelFactory)
         {
             Logger = this.Log();
             View = view ?? throw new ArgumentNullException(nameof(view));
-            Factory = viewModelFactory ?? ViewModelFactory.Current;
+            Factory = viewModelFactory;
             ModalSubject = new BehaviorSubject<IImmutableList<IViewModel>>(ImmutableList<IViewModel>.Empty);
             PageSubject = new BehaviorSubject<IImmutableList<IViewModel>>(ImmutableList<IViewModel>.Empty);