Delphi/Lazarus: Set ModalResult without Button programmatically

I am using a Form containing two buttons setting the ModalResult to mrOk or mrCancel. That is working perfectly. I am showing the form calling ShowModal and whenever the user clicks on one of the buttons, the window closes automatically and I can evaluate the result.

Now, I also want to allow the user to not only click on the button in order to close the window, but also to use a keyboard shortcut to do so. For this, I have set KeyPreview to true in the forms properties and I have defined the following procedure.

procedure TForm2.FormKeyDown(Sender: TObject; var Key: Word; 
   Shift: TShiftState);
begin

  if key = ord(#13) then begin
     ModalResult := mrOk;
     Close;
  end;

end; 

The invocation is done in the following way:

if Form2.ShowModal = mrOk then begin
   // Code after Okay
end else begin
   // Code after Cancel
end;

Unfortunately, this is not working at all. The ModalResult always remains mrNone although I have set it to mrOk. What am I doing wrong here?