diff --git a/lcl/include/customnotebook.inc b/lcl/include/customnotebook.inc
index b5d02a97e0..8a98e33e0b 100644
--- a/lcl/include/customnotebook.inc
+++ b/lcl/include/customnotebook.inc
@@ -321,19 +321,19 @@ end;
 function TCustomNotebook.CanChangePageIndex: boolean;
 begin
   Result := True;
-  if ([csDestroying] * ComponentState = []) and Assigned(OnChanging) then
-    OnChanging(Self,Result);
+  if ([csDesigning, csDestroying] * ComponentState = []) and Assigned(OnChanging) then
+    OnChanging(Self, Result);
 end;
 
 function TCustomNotebook.GetMinimumTabWidth: integer;
 begin
-  Result:=TWSCustomNotebookClass(WidgetSetClass).GetNotebookMinTabWidth(Self);
+  Result := TWSCustomNotebookClass(WidgetSetClass).GetNotebookMinTabWidth(Self);
   //debugln('TCustomNotebook.GetMinimumTabWidth A ',dbgs(Result));
 end;
 
 function TCustomNotebook.GetMinimumTabHeight: integer;
 begin
-  Result:=TWSCustomNotebookClass(WidgetSetClass).GetNotebookMinTabHeight(Self);
+  Result := TWSCustomNotebookClass(WidgetSetClass).GetNotebookMinTabHeight(Self);
   //debugln('TCustomNotebook.GetMinimumTabHeight A ',dbgs(Result));
 end;
 
@@ -770,9 +770,9 @@ end;
 procedure TCustomNotebook.CNNotify(var Message: TLMNotify);
 var
   OldPageIndex: LongInt;
-Begin
+begin
   with Message do
-    Case NMHdr^.code of
+    case NMHdr^.code of
       TCN_SELCHANGE:
         begin
           // set the page from the NMHDR^.idfrom
diff --git a/lcl/interfaces/gtk/gtkcallback.inc b/lcl/interfaces/gtk/gtkcallback.inc
index 19964ab0af..9413114fef 100644
--- a/lcl/interfaces/gtk/gtkcallback.inc
+++ b/lcl/interfaces/gtk/gtkcallback.inc
@@ -1988,39 +1988,41 @@ function GtkSwitchPage(widget: PGtkWidget; page: Pgtkwidget; pagenum: integer;
 var
   Mess: TLMNotify;
   NMHdr: tagNMHDR;
-  SwitchAllowed: Boolean;
 begin
   Result := CallBackDefaultReturn;
 
-  if (Widget=nil) or (Page=nil) then ;
-
   EventTrace('switch-page', data);
   UpdateNoteBookClientWidget(TObject(Data));
+  
+  if PGtkNotebook(Widget)^.cur_page = nil then // for windows compatibility
+    Exit;
 
   // gtkswitchpage is called before the switch
 
   // send first the TCN_SELCHANGING to ask if switch is allowed
-  FillChar(Mess,SizeOf(Mess),0);
+  FillChar(Mess, SizeOf(Mess), 0);
   Mess.Msg := LM_NOTIFY;
-  FillChar(NMHdr,SizeOf(NMHdr),0);
+  FillChar(NMHdr, SizeOf(NMHdr), 0);
   NMHdr.code := TCN_SELCHANGING;
-  NMHdr.hwndfrom := PtrUInt(widget);
-  NMHdr.idfrom := pagenum;  //use this to set pageindex to the correct page.
+  NMHdr.hwndFrom := PtrUInt(widget);
+  NMHdr.idFrom := pagenum;  //use this to set pageindex to the correct page.
   Mess.NMHdr := @NMHdr;
   Mess.Result := 0;
   DeliverMessage(Data, Mess);
-  SwitchAllowed:=Mess.Result=0;
-  if not SwitchAllowed then begin
-    debugln('gtkswitchpage A SwitchAllowed=false not yet implemented');
+  if Mess.Result <> 0 then
+  begin
+    g_signal_stop_emission_by_name(PGtkObject(Widget), 'switch-page');
+    Result := not CallBackDefaultReturn;
+    Exit;
   end;
 
   // then send the new page
-  FillChar(Mess,SizeOf(Mess),0);
+  FillChar(Mess, SizeOf(Mess), 0);
   Mess.Msg := LM_NOTIFY;
-  FillChar(NMHdr,SizeOf(NMHdr),0);
+  FillChar(NMHdr, SizeOf(NMHdr), 0);
   NMHdr.code := TCN_SELCHANGE;
-  NMHdr.hwndfrom := PtrUInt(widget);
-  NMHdr.idfrom := pagenum;  //use this to set pageindex to the correct page.
+  NMHdr.hwndFrom := PtrUInt(widget);
+  NMHdr.idFrom := pagenum;  //use this to set pageindex to the correct page.
   Mess.NMHdr := @NMHdr;
   DeliverMessage(Data, Mess);
 end;
diff --git a/lcl/interfaces/qt/qtwidgets.pas b/lcl/interfaces/qt/qtwidgets.pas
index 4690596d1f..90c4a93374 100644
--- a/lcl/interfaces/qt/qtwidgets.pas
+++ b/lcl/interfaces/qt/qtwidgets.pas
@@ -584,6 +584,7 @@ type
     
     function EventFilter(Sender: QObjectH; Event: QEventH): Boolean; cdecl; override;
     procedure SignalCurrentChanged(Index: Integer); cdecl;
+    function SlotTabBarMouse(Sender: QObjectH; Event: QEventH): Boolean; cdecl;
   public
     function indexOf(const AWidget: QWidgetH): integer;
     function insertTab(index: Integer; page: QWidgetH; p2: WideString): Integer; overload;
@@ -4800,6 +4801,7 @@ var
   Method: TMethod;
 begin
   inherited AttachEvents;
+
   FCurrentChangedHook := QTabWidget_hook_create(Widget);
   FTabBarEventHook := QWidget_hook_create(TabBar);
 
@@ -4831,7 +4833,7 @@ begin
       QEventKeyRelease: SlotKey(Sender, Event);
       QEventMouseButtonPress,
       QEventMouseButtonRelease,
-      QEventMouseButtonDblClick: SlotMouse(Sender, Event);
+      QEventMouseButtonDblClick: Result := SlotTabBarMouse(Sender, Event);
     else
       QEvent_ignore(Event);
     end;
@@ -4935,18 +4937,53 @@ var
 begin
   if LCLObject = nil then
     Exit;
-  FillChar(Msg, SizeOf(Msg), #0);
+    
+  FillChar(Msg, SizeOf(Msg), 0);
+  Msg.Msg := LM_NOTIFY;
+  FillChar(Hdr, SizeOf(Hdr), 0);
 
-  Msg.Msg := CN_NOTIFY;
-  
   Hdr.hwndFrom := LCLObject.Handle;
   Hdr.Code := TCN_SELCHANGE;
   Hdr.idFrom := Index;
-  
   Msg.NMHdr := @Hdr;
+  Msg.Result := 0;
   DeliverMessage(Msg);
 end;
 
+function TQtTabWidget.SlotTabBarMouse(Sender: QObjectH; Event: QEventH): Boolean; cdecl;
+var
+  MousePos: TQtPoint;
+  NewIndex, CurIndex: Integer;
+  Msg: TLMNotify;
+  Hdr: TNmHdr;
+begin
+  Result := False;
+  MousePos := QMouseEvent_pos(QMouseEventH(Event))^;
+  NewIndex := QTabBar_tabAt(QTabBarH(Sender), @MousePos);
+  CurIndex := QTabBar_currentIndex(QTabBarH(Sender));
+  if (NewIndex <> CurIndex) and (NewIndex <> -1) and (CurIndex <> -1) then
+  begin
+    FillChar(Msg, SizeOf(Msg), 0);
+    Msg.Msg := LM_NOTIFY;
+    FillChar(Hdr, SizeOf(Hdr), 0);
+
+    Hdr.hwndFrom := LCLObject.Handle;
+    Hdr.Code := TCN_SELCHANGING;
+    Hdr.idFrom := CurIndex;
+    Msg.NMHdr := @Hdr;
+    Msg.Result := 0;
+    DeliverMessage(Msg);
+
+    if Msg.Result <> 0 then
+    begin
+      QEvent_accept(Event);
+      Result := True;
+      Exit;
+    end;
+  end;
+  SlotMouse(Sender, Event);
+end;
+
 function TQtTabWidget.indexOf(const AWidget: QWidgetH): integer;
 begin
   Result := QTabWidget_indexOf(QTabWidgetH(Widget), AWidget);