diff --git a/lcl/interfaces/qt/qtint.pp b/lcl/interfaces/qt/qtint.pp
index 728a062cf9..5d80c60392 100644
--- a/lcl/interfaces/qt/qtint.pp
+++ b/lcl/interfaces/qt/qtint.pp
@@ -266,13 +266,11 @@ type
   procedure MapX11Window(AWinID: LongWord);
   {$IFDEF QtUseAccurateFrame}
   function GetX11SupportedAtoms(AWinID: LongWord; AList: TStrings): boolean;
-  {will be used for shadow sizes and getWindowFrameSize after testing}
+  {Ask for _NET_FRAME_EXTENTS,_KDE_NET_WM_SHADOW,_GTK_NET_FRAME_EXTENTS}
   function GetX11RectForAtom(AWinID: LongWord; const AAtomName: string; out ARect: TRect): boolean;
   function GetX11WindowPos(AWinID: LongWord; out ALeft, ATop: integer): boolean;
   {check if wm supports request for frame extents}
   function AskX11_NET_REQUEST_FRAME_EXTENTS(AWinID: LongWord; out AMargins: TRect): boolean;
-  {trial to get real frame size on X11 before window is visible by using _NET_FRAME_EXTENTS}
-  function GetWindowFrameSize(AWinID: LongWord; out ALeft, ATop, ARight, ABottom: integer): Boolean;
   {$ENDIF}
   {$ENDIF}
 
diff --git a/lcl/interfaces/qt/qtobject.inc b/lcl/interfaces/qt/qtobject.inc
index bfbfd72f92..4c1a507dd6 100644
--- a/lcl/interfaces/qt/qtobject.inc
+++ b/lcl/interfaces/qt/qtobject.inc
@@ -1942,12 +1942,12 @@ begin
       QApplication_syncX();
     end;
 
-    if not B and not GetWindowFrameSize(AID, R.Left, R.Top, R.Right, R.Bottom) then
+    if not B and not GetX11RectForAtom(AID, '_NET_FRAME_EXTENTS', R) then
     begin
       AId := QWidget_winID(ATempWidget);
       I := 0;
       ATicks := GetTickCount;
-      while not GetWindowFrameSize(AID, R.Left, R.Top, R.Right, R.Bottom) do
+      while not GetX11RectForAtom(AID, '_NET_FRAME_EXTENTS', R) do
       begin
         QApplication_syncX();
         QCoreApplication_processEvents;
diff --git a/lcl/interfaces/qt/qtwidgets.pas b/lcl/interfaces/qt/qtwidgets.pas
index c79017efd7..4651a82c06 100644
--- a/lcl/interfaces/qt/qtwidgets.pas
+++ b/lcl/interfaces/qt/qtwidgets.pas
@@ -7363,9 +7363,10 @@ begin
             R := QtWidgetSet.WSFrameMargins;
             if (R.Left = 0) and (R.Top = 0) and (R.Bottom = 0) and (R.Right = 0) then
             begin
-              GetWindowFrameSize(QWidget_winID(Widget), R.Left, R.Top, R.Right, R.Bottom);
+              GetX11RectForAtom(QWidget_winID(Widget),'_NET_FRAME_EXTENTS', R);
               QtWidgetSet.WSFrameMargins := R;
               FrameMargins := R;
+              DebugLn('WARNING: TQtMainWindow.EventFilter('+dbgsName(LCLObject)+') setting widgetset frame margins to '+dbgs(R)+' from form activation !');
             end else
             begin
               if QX11Info_isCompositingManagerRunning then
diff --git a/lcl/interfaces/qt/qtx11.inc b/lcl/interfaces/qt/qtx11.inc
index 89c42c6f7d..cf58c418a9 100644
--- a/lcl/interfaces/qt/qtx11.inc
+++ b/lcl/interfaces/qt/qtx11.inc
@@ -375,76 +375,6 @@ begin
   Result := (AXWinAttr.map_installed > 0) and (AXWinAttr.map_state = 2);
 end;
 
-function GetWindowFrameSize(AWinID: LongWord; out ALeft, ATop, ARight,
-  ABottom: integer): Boolean;
-var
-  Display: PDisplay;
-  X11Window: TWindow;
-  WMAtom: TAtom;
-  typeReturned: TAtom;
-  formatReturned: Integer;
-  nitemsReturned: PtrInt;
-  unused: PtrInt;
-  data: Pointer;
-  ANewData: PUInt32;
-begin
-
-  Result := False;
-  Display := QX11Info_display();
-  ALeft := 0;
-  ATop := 0;
-  ARight := 0;
-  ABottom := 0;
-  if Display = nil then
-    exit;
-
-  X11Window := TWindow(AWinID);
-  if X11Window = 0 then
-    exit;
-
-  {TODO: compositing wm must provide shadow decorations _KDE_NET_WM_SHADOW, find others}
-  WMAtom := XInternAtom(Display,'_NET_FRAME_EXTENTS', True);
-  if WMAtom > 0 then
-  begin
-    data := nil;
-    if XGetWindowProperty(Display, X11Window, WMAtom, 0, 4, False, XA_CARDINAL,
-      @typeReturned, @formatReturned, @nitemsReturned,
-      @unused, @data) = Success then
-    begin
-      if (typeReturned = XA_CARDINAL) and (formatReturned = 32) and
-        (Data <> nil) then
-      begin
-        ANewData := Data;
-        while nitemsReturned > 0 do
-        begin
-          if ALeft = 0 then
-            ALeft := Integer(ANewData^)
-          else
-          if ARight = 0 then
-            ARight := Integer(ANewData^)
-          else
-          if ATop = 0 then
-            ATop := Integer(ANewData^)
-          else
-          if ABottom = 0 then
-            ABottom := Integer(ANewData^);
-          dec(nItemsReturned);
-          if Result or (nItemsReturned = 0) then
-            break;
-          inc(ANewData);
-        end;
-        Result := True;
-        if nitemsReturned > 0 then
-          XFree(Data);
-        Data := nil;
-      end;
-    end;
-  end else
-  begin
-    DebugLn('QtLCL error: "'+GetWindowManager+'" wm does not support _NET_FRAME_EXTENTS (1).');
-  end;
-end;
-
 var
   InternalExtentsAtom: TAtom = 0; {find extents atom}
   InternalExtentsCounter: Integer = 0; {counter for bad wm, eg for blackbox}
@@ -517,7 +447,7 @@ begin
       if XIfEvent(d, @ReturnEvent,
         @propNotifyFrameExtents, TXPointer(@AWinID)) = Success then
       begin
-        Result := GetWindowFrameSize(AWinID, AMargins.Left, AMargins.Top, AMargins.Right, AMargins.Bottom);
+        Result := GetX11RectForAtom(AWinID, '_NET_FRAME_EXTENTS', AMargins);
         if not Result and (InternalExtentsCounter = -BadImplementation) then
         begin
           DebugLn('QtLCL WARNING: "'+GetWindowManager+'" wm bad implementation of _NET_REQUEST_FRAME_EXTENTS.');