diff --git a/Resources/InsaneWidget/XInsaneWidget.cpp b/Resources/InsaneWidget/XInsaneWidget.cpp
index 4c823e7..bc58d3c 100644
--- a/Resources/InsaneWidget/XInsaneWidget.cpp
+++ b/Resources/InsaneWidget/XInsaneWidget.cpp
@@ -422,10 +422,9 @@ void XInsaneWidget::Setup(wxConfig * config, TimeredStatusBar * sb)
   btnScan->Enable(false);
   btnScan->Bind ( wxEVT_RIGHT_UP, &XInsaneWidget::OnBtnScanRightClick, this );
   btnScan->Bind ( wxEVT_LEFT_UP, &XInsaneWidget::OnBtnScanClick, this );
-  m_backgroundScannerDiscoveryEvh = std::make_unique<BackgroundScannerDiscoveryEVH>(this);
-  BackgroundScannerDiscovery * backgroundDiscovery = new BackgroundScannerDiscovery ( m_scannerWidget.get(),
-                                                                                      m_backgroundScannerDiscoveryEvh.get());
-  backgroundDiscovery->Run();
+  m_backgroundDiscovery = new BackgroundScannerDiscovery ( m_scannerWidget.get(),
+                                                          new BackgroundScannerDiscoveryEVH(this)); // Takes ownership.
+  m_backgroundDiscovery->Run();
 }
 
 
@@ -581,5 +580,14 @@ void XInsaneWidget::CancelScanning()
 
 void XInsaneWidget::EnableScanButton(bool enable)
 {
+  // Called from BackgroundScannerDiscoveryEVH::Done() only;
   btnScan->Enable(enable);
+  m_backgroundDiscovery = nullptr;
+}
+
+bool XInsaneWidget::IsScannerDiscoveryRunning()
+{
+  if (!m_backgroundDiscovery)
+    return false;
+  return m_backgroundDiscovery->IsRunning();
 }
diff --git a/Resources/InsaneWidget/XInsaneWidget.h b/Resources/InsaneWidget/XInsaneWidget.h
index ca75455..69d2e0f 100644
--- a/Resources/InsaneWidget/XInsaneWidget.h
+++ b/Resources/InsaneWidget/XInsaneWidget.h
@@ -23,7 +23,7 @@
 #include <memory>
 #include <vector>
 
-class BackgroundScannerDiscoveryEVH;
+class BackgroundScannerDiscovery; // Is a wxThread.
 class ScanProjectHandler; // An event handler extending InsaneWorkerEvent.
 class XStampWidget;
 struct StampDescriptor;
@@ -66,6 +66,7 @@ public:
   void CancelScanning();
   void EnableScanButton(bool enable); // For CallAfter.
   void Setup(wxConfig * config, TimeredStatusBar * sb);
+  bool IsScannerDiscoveryRunning();
 private:
   wxConfig * m_config;
   wxWeakRef<TimeredStatusBar> m_sb;
@@ -81,7 +82,7 @@ private:
   // Available devices and minimal options.
   std::unique_ptr<XScannerWidget> m_scannerWidget;
   std::unique_ptr<InsaneWorker> m_insaneWorker;
-  std::unique_ptr<BackgroundScannerDiscoveryEVH> m_backgroundScannerDiscoveryEvh;
+  BackgroundScannerDiscovery * m_backgroundDiscovery;
   std::unique_ptr<ScanProjectHandler> m_scanProject;
 
   bool m_doubleSided = false;
diff --git a/Resources/InsaneWidget/XScannerWidget.cpp b/Resources/InsaneWidget/XScannerWidget.cpp
index 2abb0d2..ed93070 100644
--- a/Resources/InsaneWidget/XScannerWidget.cpp
+++ b/Resources/InsaneWidget/XScannerWidget.cpp
@@ -311,7 +311,10 @@ wxThread::ExitCode BackgroundScannerDiscovery::Entry()
     evt.SetShow ( true );
     m_owner->OnActivated ( evt );
     if (m_evh)
+    {
       m_evh->OnDone();
+      wxDELETE(m_evh);
+    }
   }
   return ( wxThread::ExitCode ) 0;
 }
@@ -321,3 +324,5 @@ wxThread::ExitCode BackgroundScannerDiscovery::Entry()
 void BackgroundScannerDiscoveryEvent::OnDone()
 {}
 
+BackgroundScannerDiscoveryEvent::~BackgroundScannerDiscoveryEvent() = default;
+
diff --git a/Resources/InsaneWidget/XScannerWidget.h b/Resources/InsaneWidget/XScannerWidget.h
index 55282a8..b6b6323 100644
--- a/Resources/InsaneWidget/XScannerWidget.h
+++ b/Resources/InsaneWidget/XScannerWidget.h
@@ -99,7 +99,7 @@ public:
   BackgroundScannerDiscovery ( XScannerWidget * owner, BackgroundScannerDiscoveryEvent * evh )
   {
     m_owner = owner;
-    m_evh = evh;
+    m_evh = evh; // Owned here.
   }
   virtual ~BackgroundScannerDiscovery() {};
   virtual ExitCode Entry();
@@ -112,6 +112,7 @@ class BackgroundScannerDiscoveryEvent
 {
 public:
   virtual void OnDone();
+  virtual ~BackgroundScannerDiscoveryEvent();
 
 };
 
diff --git a/XS7.cpp b/XS7.cpp
index 26e2afa..d1501ce 100644
--- a/XS7.cpp
+++ b/XS7.cpp
@@ -49,6 +49,8 @@ void XS7::Setup(wxConfig * config)
   wxString fixedTip = _("'Shift + left' click to generate a new destination file name.");
   fixedTip += _T("\n") + m_insaneWidget->lblNewDoc->GetToolTipText();
   m_insaneWidget->lblNewDoc->SetToolTip(fixedTip);
+
+  Bind(wxEVT_CLOSE_WINDOW, &XS7::OnClose, this);
 }
 
 XS7::~XS7()
@@ -57,6 +59,27 @@ XS7::~XS7()
     MiscTools::SaveSizePos(m_config, this, wxString("/") + _APPNAME_);
 }
 
+void XS7::OnClose(wxCloseEvent& evt)
+{
+  if (!m_insaneWidget)
+  {
+    evt.Skip();
+    return;
+  }
+  if (m_insaneWidget->IsScannerDiscoveryRunning())
+  {
+    evt.Veto();
+    TimeredStatusBar * sb = static_cast<TimeredStatusBar*> (GetStatusBar());
+    if (sb)
+      sb->SetTransientText(_("Veto: scanner discovery is running."));
+    evt.Skip(false);
+    return;
+  }
+  evt.Skip();
+  
+}
+
+
 void XS7::OnDpkRepositoryChange ( wxFileDirPickerEvent& evt )
 {
   m_config->Write ( _T ( "/DocRoot" ), dpkDestination->GetPath() );
diff --git a/XS7.h b/XS7.h
index 190871e..2154fa9 100644
--- a/XS7.h
+++ b/XS7.h
@@ -33,6 +33,7 @@ private:
   void OnDpkDoubleClick ( wxMouseEvent& evt );
   void OnAppKeyPressed(wxKeyEvent& evt);
   void OnNewDocLeftClick ( wxMouseEvent& evt ); // wxStaticText in m_insaneWidget.
+  void OnClose(wxCloseEvent& evt);
   void OnAbout(wxMouseEvent& evt);
 };