diff --git a/lcl/forms.pp b/lcl/forms.pp
index ca2ab73ac1..3b6a6119f7 100644
--- a/lcl/forms.pp
+++ b/lcl/forms.pp
@@ -533,6 +533,8 @@ type
     procedure Notification(AComponent: TComponent; Operation : TOperation);override;
     procedure PaintWindow(dc : Hdc); override;
     procedure RequestAlign; override;
+    procedure CalculatePreferredSize(var PreferredWidth,
+           PreferredHeight: integer; WithThemeSpace: Boolean); override;
     procedure SetZOrder(Topmost: Boolean); override;
     procedure SetParent(NewParent: TWinControl); override;
     procedure MoveToDefaultPosition; virtual;
diff --git a/lcl/include/customform.inc b/lcl/include/customform.inc
index fe70b36b7c..5fdef192b7 100644
--- a/lcl/include/customform.inc
+++ b/lcl/include/customform.inc
@@ -1042,6 +1042,23 @@ Begin
   inherited RequestAlign;
 end;
 
+procedure TCustomForm.CalculatePreferredSize(var PreferredWidth,
+  PreferredHeight: integer; WithThemeSpace: Boolean);
+var
+  WorkArea: TRect;
+begin
+  inherited CalculatePreferredSize(PreferredWidth, PreferredHeight,
+    WithThemeSpace);
+  if Anchors*[akRight,akBottom]<>[] then begin
+    // do size bigger than the monitor workarea
+    WorkArea:=Monitor.WorkareaRect;
+    if akRight in Anchors then
+      PreferredWidth:=min(PreferredWidth,WorkArea.Right-WorkArea.Left);
+    if akBottom in Anchors then
+      PreferredHeight:=min(PreferredHeight,WorkArea.Bottom-WorkArea.Top);
+  end;
+end;
+
 {------------------------------------------------------------------------------
        TCustomForm SetDesigner
 ------------------------------------------------------------------------------}