diff --git a/lcl/interfaces/qt/qtwidgets.pas b/lcl/interfaces/qt/qtwidgets.pas
index 2ec576d05e..91056a706d 100644
--- a/lcl/interfaces/qt/qtwidgets.pas
+++ b/lcl/interfaces/qt/qtwidgets.pas
@@ -7020,6 +7020,9 @@ end;
 procedure TQtMainWindow.ChangeParent(NewParent: QWidgetH);
 var
   Flags: QtWindowFlags;
+  {$IFNDEF MSWINDOWS}
+  Flags2: QtWindowFlags;
+  {$ENDIF}
   Visible: Boolean;
 begin
   if NewParent <> Widget then
@@ -7027,6 +7030,15 @@ begin
     Visible := getVisible;
     Flags := windowFlags;
     setParent(NewParent);
+    {$IFNDEF MSWINDOWS}
+    //issue #40440
+    if NewParent <> nil then
+      Flags2 := QWidget_windowFlags(NewParent)
+    else
+      Flags2 := 0;
+    if (Flags and QtWindowStaysOnTopHint = 0) and (Flags2 and QtWindowStaysOnTopHint <> 0) then
+      Flags := Flags or QtWindowStaysOnTopHint;
+    {$ENDIF}
     setWindowFlags(Flags);
     setVisible(Visible);
   end;
diff --git a/lcl/interfaces/qt5/qtwidgets.pas b/lcl/interfaces/qt5/qtwidgets.pas
index 090fae29a4..52880d6d63 100644
--- a/lcl/interfaces/qt5/qtwidgets.pas
+++ b/lcl/interfaces/qt5/qtwidgets.pas
@@ -7135,6 +7135,9 @@ end;
 procedure TQtMainWindow.ChangeParent(NewParent: QWidgetH);
 var
   Flags: QtWindowFlags;
+  {$IFNDEF MSWINDOWS}
+  Flags2: QtWindowFlags;
+  {$ENDIF}
   Visible: Boolean;
 begin
   if NewParent <> Widget then
@@ -7142,6 +7145,15 @@ begin
     Visible := getVisible;
     Flags := windowFlags;
     setParent(NewParent);
+    {$IFNDEF MSWINDOWS}
+    //issue #40440
+    if NewParent <> nil then
+      Flags2 := QWidget_windowFlags(NewParent)
+    else
+      Flags2 := 0;
+    if (Flags and QtWindowStaysOnTopHint = 0) and (Flags2 and QtWindowStaysOnTopHint <> 0) then
+      Flags := Flags or QtWindowStaysOnTopHint;
+    {$ENDIF}
     setWindowFlags(Flags);
     setVisible(Visible);
   end;
diff --git a/lcl/interfaces/qt6/qtwidgets.pas b/lcl/interfaces/qt6/qtwidgets.pas
index 70f875dc5e..3972acac25 100644
--- a/lcl/interfaces/qt6/qtwidgets.pas
+++ b/lcl/interfaces/qt6/qtwidgets.pas
@@ -7159,6 +7159,9 @@ end;
 procedure TQtMainWindow.ChangeParent(NewParent: QWidgetH);
 var
   Flags: QtWindowFlags;
+  {$IFNDEF MSWINDOWS}
+  Flags2: QtWindowFlags;
+  {$ENDIF}
   Visible: Boolean;
 begin
   if NewParent <> Widget then
@@ -7166,6 +7169,15 @@ begin
     Visible := getVisible;
     Flags := windowFlags;
     setParent(NewParent);
+    {$IFNDEF MSWINDOWS}
+    //issue #40440
+    if NewParent <> nil then
+      Flags2 := QWidget_windowFlags(NewParent)
+    else
+      Flags2 := 0;
+    if (Flags and QtWindowStaysOnTopHint = 0) and (Flags2 and QtWindowStaysOnTopHint <> 0) then
+      Flags := Flags or QtWindowStaysOnTopHint;
+    {$ENDIF}
     setWindowFlags(Flags);
     setVisible(Visible);
   end;