diff --git a/designer/designer.pp b/designer/designer.pp
index bb80bb0035..b228f72e7f 100644
--- a/designer/designer.pp
+++ b/designer/designer.pp
@@ -2507,7 +2507,9 @@ end;
 procedure TDesigner.SetMediator(const AValue: TDesignerMediator);
 begin
   if FMediator=AValue then exit;
+  if FMediator<>nil then FMediator.Designer:=nil;
   FMediator:=AValue;
+  if FMediator<>nil then FMediator.Designer:=Self;
 end;
 
 procedure TDesigner.SetShowEditorHints(const AValue: boolean);
diff --git a/designer/noncontroldesigner.pas b/designer/noncontroldesigner.pas
index d13ae23186..b1507f6f8d 100644
--- a/designer/noncontroldesigner.pas
+++ b/designer/noncontroldesigner.pas
@@ -43,6 +43,7 @@ type
   private
     FFrameWidth: integer;
     FMediator: TDesignerMediator;
+    procedure SetMediator(const AValue: TDesignerMediator);
   protected
     procedure SetFrameWidth(const AValue: integer); virtual;
   public
@@ -53,7 +54,7 @@ type
     procedure DoSaveBounds; override;
   public
     property FrameWidth: integer read FFrameWidth write SetFrameWidth;
-    property Mediator: TDesignerMediator read FMediator write FMediator;
+    property Mediator: TDesignerMediator read FMediator write SetMediator;
   end;
   
   
@@ -62,6 +63,14 @@ implementation
 
 { TNonControlDesignerForm }
 
+procedure TNonControlDesignerForm.SetMediator(const AValue: TDesignerMediator);
+begin
+  if FMediator=AValue then exit;
+  if FMediator<>nil then FMediator.LCLForm:=nil;
+  FMediator:=AValue;
+  if FMediator<>nil then FMediator.LCLForm:=Self;
+end;
+
 procedure TNonControlDesignerForm.SetFrameWidth(const AValue: integer);
 begin
   if FFrameWidth = AValue then 
diff --git a/ideintf/formeditingintf.pas b/ideintf/formeditingintf.pas
index e809f2abf0..bb9cd4e70b 100644
--- a/ideintf/formeditingintf.pas
+++ b/ideintf/formeditingintf.pas
@@ -90,10 +90,21 @@ type
     which will emulate the painting, handle the mouse and editing bounds. }
 
   TDesignerMediator = class(TComponent)
+  private
+    FDesigner: TComponentEditorDesigner;
+    FLCLForm: TForm;
+  protected
+    procedure SetDesigner(const AValue: TComponentEditorDesigner);
+    procedure SetLCLForm(const AValue: TForm); virtual;
   public
     class function FormClass: TComponentClass; virtual; abstract;
     class function CreateMediator(TheOwner, aForm: TComponent): TDesignerMediator; virtual; abstract;
     class procedure InitFormInstance(aForm: TComponent); virtual; // called after NewInstance, before constructor
+  public
+    procedure SetBounds(AComponent: TComponent; NewBounds: TRect); virtual; abstract;
+    procedure GetBounds(AComponent: TComponent; out CurBounds: TRect); virtual; abstract;
+    property LCLForm: TForm read FLCLForm write SetLCLForm;
+    property Designer: TComponentEditorDesigner read FDesigner write SetDesigner;
   end;
   TDesignerMediatorClass = class of TDesignerMediator;
 
@@ -182,6 +193,19 @@ implementation
 
 { TDesignerMediator }
 
+procedure TDesignerMediator.SetDesigner(const AValue: TComponentEditorDesigner
+  );
+begin
+  if FDesigner=AValue then exit;
+  FDesigner:=AValue;
+end;
+
+procedure TDesignerMediator.SetLCLForm(const AValue: TForm);
+begin
+  if FLCLForm=AValue then exit;
+  FLCLForm:=AValue;
+end;
+
 class procedure TDesignerMediator.InitFormInstance(aForm: TComponent);
 begin