diff --git a/designer/designer.pp b/designer/designer.pp
index ea001b355f..19d1c5e64a 100644
--- a/designer/designer.pp
+++ b/designer/designer.pp
@@ -100,10 +100,8 @@ type
     FDesignerPopupMenu: TPopupMenu;
     FDefaultFormBounds: TRect;
     FLastFormBounds: TRect;
-    FDefaultFormBoundsValid: boolean;
     FFlags: TDesignerFlags;
     FGridColor: TColor;
-    FLookupRoot: TComponent;
     FMediator: TDesignerMediator;
     FOnPastedComponents: TOnPastedComponents;
     FProcessingDesignerEvent: Integer;
@@ -275,7 +273,7 @@ type
     DDC: TDesignerDeviceContext;
 
     constructor Create(TheDesignerForm: TCustomForm; AControlSelection: TControlSelection);
-    procedure PrepareFreeDesigner(AFreeComponent: boolean);
+    procedure PrepareFreeDesigner(AFreeComponent: boolean); override;
     procedure DisconnectComponent; override;
     destructor Destroy; override;
 
@@ -346,7 +344,6 @@ type
     property GridSizeY: integer read GetGridSizeY write SetGridSizeY;
     property GridColor: TColor read GetGridColor write SetGridColor;
     property IsControl: Boolean read GetIsControl write SetIsControl;
-    property LookupRoot: TComponent read FLookupRoot;
     property Mediator: TDesignerMediator read FMediator write SetMediator;
     property ProcessingDesignerEvent: Integer read FProcessingDesignerEvent;
     property OnActivated: TNotifyEvent read FOnActivated write FOnActivated;
@@ -386,8 +383,6 @@ type
     property SnapToGrid: boolean read GetSnapToGrid write SetSnapToGrid;
     property TheFormEditor: TCustomFormEditor read FTheFormEditor write FTheFormEditor;
     property DefaultFormBounds: TRect read FDefaultFormBounds write SetDefaultFormBounds;
-    property DefaultFormBoundsValid: boolean read FDefaultFormBoundsValid
-                                             write FDefaultFormBoundsValid;
   end;
 
 const
diff --git a/ide/sourcefilemanager.pas b/ide/sourcefilemanager.pas
index 90eb98c173..3d3f23c126 100644
--- a/ide/sourcefilemanager.pas
+++ b/ide/sourcefilemanager.pas
@@ -35,22 +35,22 @@ uses
   LCLType, LCLProc, FileProcs, FileUtil, IDEProcs, DialogProcs, IDEDialogs,
   LConvEncoding, LazFileCache, LResources, PropEdits, DefineTemplates,
   IDEMsgIntf, IDEProtocol, LazarusIDEStrConsts, NewDialog, NewProjectDlg,
-  LazIDEIntf, MainBase, MainBar, MainIntf, MenuIntf, NewItemIntf, ProjectIntf,
-  Project, ProjectDefs, ProjectInspector, CompilerOptions, BasePkgManager,
-  PackageIntf, PackageDefs, PackageSystem, SrcEditorIntf, IDEWindowIntf,
+  LazIDEIntf, MainBase, MainBar, MainIntf, MenuIntf, NewItemIntf,
+  CompOptsIntf, SrcEditorIntf, IDEWindowIntf,
+  ProjectIntf, Project, ProjectDefs, ProjectInspector,
+  PackageIntf, PackageDefs, PackageSystem, CompilerOptions, BasePkgManager,
   ComponentReg, SourceEditor, EditorOptions, CustomFormEditor, FormEditor,
   EmptyMethodsDlg, BaseDebugManager, ControlSelection, TransferMacros,
-  EnvironmentOpts, BuildManager, Designer, EditorMacroListViewer, KeywordFuncLists,
+  EnvironmentOpts, BuildManager, EditorMacroListViewer, KeywordFuncLists,
   FindRenameIdentifier, GenericCheckList, ViewUnit_Dlg, DiskDiffsDialog,
-  {$IFNDEF EnableOldExtTools}
-  etMessagesWnd,
-  {$ELSE}
-  MsgView,
-  {$ENDIF}
   InputHistory, CheckLFMDlg, LCLMemManager, CodeToolManager, CodeToolsStructs,
   ConvCodeTool, CodeCache, CodeTree, FindDeclarationTool, BasicCodeTools,
   SynEdit, UnitResources, IDEExternToolIntf, ExtToolDialog, PublishModule,
-  CompOptsIntf;
+{$IFNDEF EnableOldExtTools}
+  etMessagesWnd;
+{$ELSE}
+  MsgView;
+{$ENDIF}
 
 type
 
@@ -2237,7 +2237,7 @@ begin
     end;
 
     if (AnUnitInfo.Component<>nil) and (MainIDE.LastFormActivated<>nil)
-    and (TDesigner(MainIDE.LastFormActivated.Designer).LookupRoot=AnUnitInfo.Component) then
+    and (MainIDE.LastFormActivated.Designer.LookupRoot=AnUnitInfo.Component) then
       MainIDE.LastFormActivated:=nil;
 
     // save some meta data of the source
@@ -3361,7 +3361,7 @@ function TLazSourceFileManager.InitOpenedProjectFile(AFileName: string;
 var
   EditorInfoIndex, i, j: Integer;
   NewBuf: TCodeBuffer;
-  LastDesigner: TDesigner;
+  LastDesigner: TIDesigner;
   AnUnitInfo: TUnitInfo;
   HandlerResult: TModalResult;
   AnEditorInfo: TUnitEditorInfo;
@@ -3480,7 +3480,7 @@ begin
 
     // select a form (object inspector, formeditor, control selection)
     if MainIDE.LastFormActivated<>nil then begin
-      LastDesigner:=TDesigner(MainIDE.LastFormActivated.Designer);
+      LastDesigner:=MainIDE.LastFormActivated.Designer;
       debugln(['TLazSourceFileManager.InitOpenedProjectFile select form in designer: ',
                DbgSName(MainIDE.LastFormActivated),' ',DbgSName(MainIDE.LastFormActivated.Designer)]);
       LastDesigner.SelectOnlyThisComponent(LastDesigner.LookupRoot);
@@ -4625,7 +4625,7 @@ var
   Writer: TWriter;
   ACaption, AText: string;
   CompResourceCode, LFMFilename, TestFilename: string;
-  ADesigner: TDesigner;
+  ADesigner: TIDesigner;
   Grubber: TLRTGrubber;
   LRTFilename: String;
   AncestorUnit: TUnitInfo;
@@ -4914,7 +4914,7 @@ begin
     end;
   end;
   // mark designer unmodified
-  ADesigner:=FindRootDesigner(AnUnitInfo.Component) as TDesigner;
+  ADesigner:=FindRootDesigner(AnUnitInfo.Component);
   if ADesigner<>nil then
     ADesigner.DefaultFormBoundsValid:=false;
 
@@ -6640,7 +6640,7 @@ function TLazSourceFileManager.CloseUnitComponent(AnUnitInfo: TUnitInfo;
   end;
 
 var
-  OldDesigner: TDesigner;
+  OldDesigner: TIDesigner;
   AForm: TCustomForm;
   LookupRoot: TComponent;
   ComponentStillUsed: Boolean;
@@ -6678,7 +6678,7 @@ begin
 
     AForm:=FormEditor1.GetDesignerForm(LookupRoot);
     if AForm<>nil then
-      OldDesigner:=TDesigner(AForm.Designer)
+      OldDesigner:=AForm.Designer
     else
       OldDesigner:=nil;
     if MainIDE.LastFormActivated=AForm then
diff --git a/lcl/forms.pp b/lcl/forms.pp
index cd4e4dd7f3..507bbfb0ba 100644
--- a/lcl/forms.pp
+++ b/lcl/forms.pp
@@ -1642,6 +1642,9 @@ type
   { TIDesigner }
 
   TIDesigner = class(TObject)
+  protected
+    FLookupRoot: TComponent;
+    FDefaultFormBoundsValid: boolean;
   public
     function IsDesignMsg(Sender: TControl; var Message: TLMessage): Boolean;
       virtual; abstract;
@@ -1654,6 +1657,11 @@ type
     function GetShiftState: TShiftState; virtual; abstract;
     procedure SelectOnlyThisComponent(AComponent: TComponent); virtual; abstract;
     function UniqueName(const BaseName: string): string; virtual; abstract;
+    procedure PrepareFreeDesigner(AFreeComponent: boolean); virtual; abstract;
+  public
+    property LookupRoot: TComponent read FLookupRoot;
+    property DefaultFormBoundsValid: boolean read FDefaultFormBoundsValid
+                                             write FDefaultFormBoundsValid;
   end;