diff --git a/Terminal.Gui/Application.MainLoopSyncContext.cs b/Terminal.Gui/Application.MainLoopSyncContext.cs
index dfda0727ae..513608e8c1 100644
--- a/Terminal.Gui/Application.MainLoopSyncContext.cs
+++ b/Terminal.Gui/Application.MainLoopSyncContext.cs
@@ -12,7 +12,7 @@ private sealed class MainLoopSyncContext : SynchronizationContext
 
         public override void Post (SendOrPostCallback d, object state)
         {
-            MainLoop.AddIdle (
+            MainLoop?.AddIdle (
                               () =>
                               {
                                   d (state);
diff --git a/Terminal.Gui/Application.cs b/Terminal.Gui/Application.cs
index 2bde0bca09..2e6004971b 100644
--- a/Terminal.Gui/Application.cs
+++ b/Terminal.Gui/Application.cs
@@ -676,6 +676,15 @@ public static void Run (Toplevel view, Func<Exception, bool> errorHandler = null
             // by using NotifyStopRunState event.
             RunLoop (runState);
 
+            if (runState.Toplevel is null)
+            {
+#if DEBUG_IDISPOSABLE
+                Debug.Assert (_topLevels.Count == 0);
+#endif
+                runState.Dispose ();
+                return;
+            }
+
             if (!EndAfterFirstIteration)
             {
                 End (runState);
@@ -787,7 +796,7 @@ public static void RunLoop (RunState state)
 
         var firstIteration = true;
 
-        for (state.Toplevel.Running = true; state.Toplevel.Running;)
+        for (state.Toplevel.Running = true; state.Toplevel?.Running == true;)
         {
             MainLoop.Running = true;
 
@@ -838,6 +847,11 @@ public static void RunIteration (ref RunState state, ref bool firstIteration)
 
         firstIteration = false;
 
+        if (Current == null)
+        {
+            return;
+        }
+
         if (state.Toplevel != Top && (Top.NeedsDisplay || Top.SubViewNeedsDisplay || Top.LayoutNeeded))
         {
             state.Toplevel.SetNeedsDisplay (state.Toplevel.Frame);
diff --git a/UICatalog/Scenarios/BackgroundWorkerCollection.cs b/UICatalog/Scenarios/BackgroundWorkerCollection.cs
index b2a78aea19..214d453da2 100644
--- a/UICatalog/Scenarios/BackgroundWorkerCollection.cs
+++ b/UICatalog/Scenarios/BackgroundWorkerCollection.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Diagnostics;
 using System.Threading;
 using Terminal.Gui;
 
@@ -19,6 +20,10 @@ public override void Init ()
 
         //main.Dispose ();
         Application.Top.Dispose ();
+
+#if DEBUG_IDISPOSABLE
+        Debug.Assert (Application.OverlappedChildren.Count == 0);
+#endif
     }
 
     public override void Run () { }
@@ -182,6 +187,7 @@ private void OverlappedMain_Deactivate (object sender, ToplevelEventArgs top)
         {
             _workerApp?.WriteLog ($"{top.Toplevel.Data} deactivate.");
         }
+
         private void Quit () { RequestStop (); }
 
         private MenuBarItem View ()
@@ -356,6 +362,12 @@ public WorkerApp ()
             Add (_listLog);
 
             Closing += WorkerApp_Closing;
+            Closed += WorkerApp_Closed;
+        }
+
+        private void WorkerApp_Closed (object sender, ToplevelEventArgs e)
+        {
+            CancelWorker ();
         }
         private void WorkerApp_Closing (object sender, ToplevelClosingEventArgs e)
         {
@@ -474,7 +486,13 @@ public void RunWorker ()
 
                                                  _stagingsUi.Add (stagingUI);
                                                  _stagingWorkers.Remove (staging);
-
+#if DEBUG_IDISPOSABLE
+                                                 if (Application.OverlappedTop is null)
+                                                 {
+                                                     stagingUI.Dispose ();
+                                                     return;
+                                                 }
+#endif
                                                  Application.Run (stagingUI);
                                                  stagingUI.Dispose ();
                                              }