diff --git a/applications/sudoku/digitseteditor.lfm b/applications/sudoku/digitseteditor.lfm
index ee2930d41..efeba7dea 100644
--- a/applications/sudoku/digitseteditor.lfm
+++ b/applications/sudoku/digitseteditor.lfm
@@ -20,8 +20,10 @@ object DigitSetEditorForm: TDigitSetEditorForm
     AutoFill = True
     Caption = 'Digits'
     ChildSizing.LeftRightSpacing = 6
+    ChildSizing.TopBottomSpacing = 6
     ChildSizing.VerticalSpacing = 6
     ChildSizing.EnlargeHorizontal = crsScaleChilds
+    ChildSizing.EnlargeVertical = crsHomogenousChildResize
     ChildSizing.ShrinkHorizontal = crsScaleChilds
     ChildSizing.ShrinkVertical = crsScaleChilds
     ChildSizing.Layout = cclLeftToRightThenTopToBottom
@@ -40,6 +42,7 @@ object DigitSetEditorForm: TDigitSetEditorForm
       '8'
       '9'
     )
+    OnItemClick = DigitCGItemClick
     ParentBiDiMode = False
     TabOrder = 0
     Data = {
diff --git a/applications/sudoku/digitseteditor.pas b/applications/sudoku/digitseteditor.pas
index f009d6209..c86d9955a 100644
--- a/applications/sudoku/digitseteditor.pas
+++ b/applications/sudoku/digitseteditor.pas
@@ -15,17 +15,22 @@ type
   TDigitSetEditorForm = class(TForm)
     btnOK: TButton;
     DigitCG: TCheckGroup;
+    procedure DigitCGItemClick(Sender: TObject; {%H-}Index: integer);
     procedure FormActivate(Sender: TObject);
     procedure FormKeyPress(Sender: TObject; var Key: char);
     procedure FormShow(Sender: TObject);
   private
     FPreferredRight: Integer;
-    function GetDigitSet: TDigitSet;
-    procedure SetDigitSet(ASet: TDigitSet);
+    FOriginalDigitsPossible: TDigitSet;
+    function GetCurrentDigitSet: TDigitSet;
+    procedure SetCurrentDigitSet(ASet: TDigitSet);
+    procedure SetOriginalDigitsPossible(ASet: TDigitSet);
     procedure SetRight({%H-}Data: PtrInt);
+    procedure UpdateButtonState;
 
   public
-    property DigitSet: TDigitSet read GetDigitSet write SetDigitSet;
+    property CurrentDigitSet: TDigitSet read GetCurrentDigitSet write SetCurrentDigitSet;
+    property OriginalDigitsPossible: TDigitSet read FOriginalDigitsPossible write SetOriginalDigitsPossible;  //set this before CurrentDigitSet!
     property PreferredRight: Integer read FPreferredRight write FPreferredRight;
   end;
 
@@ -45,8 +50,10 @@ begin
   if (Key in ['1'..'9']) then
   begin
     Digit := Ord(Key) - Ord('0');
-    DigitCG.Checked[Pred(Digit)] := not DigitCG.Checked[Pred(Digit)];
+    if Digit in FOriginalDigitsPossible then
+      DigitCG.Checked[Pred(Digit)] := not DigitCG.Checked[Pred(Digit)];
     Key := #0;
+    UpdateButtonState;
   end;
   if (Key = #27) then //escape
   begin
@@ -67,22 +74,41 @@ begin
   ClientHeight := btnOK.Top + btnOK.Height + DigitCG.Top;
 end;
 
-function TDigitSetEditorForm.GetDigitSet: TDigitSet;
+
+procedure TDigitSetEditorForm.DigitCGItemClick(Sender: TObject; Index: integer);
+begin
+  UpdateButtonState;
+end;
+
+
+function TDigitSetEditorForm.GetCurrentDigitSet: TDigitSet;
 var
   i: Integer;
 begin
   Result := [];
   for i := 0 to DigitCG.Items.Count - 1 do
-    if DigitCG.Checked[i] then Include(Result, Succ(i));
+    if DigitCG.Checked[i] and (Succ(i) in FOriginalDigitsPossible)then Include(Result, Succ(i));
 end;
 
-procedure TDigitSetEditorForm.SetDigitSet(ASet: TDigitSet);
+procedure TDigitSetEditorForm.SetCurrentDigitSet(ASet: TDigitSet);
 var
   D: TDigits;
 begin
   for D in TDigits do
   begin
-    DigitCG.Checked[D-1] := (D in ASet);  //don't use Pred(D) here, gives RangeCheckError when D=1
+    DigitCG.Checked[D-1] := (D in ASet) and DigitCG.CheckEnabled[D-1];  //don't use Pred(D) here, gives RangeCheckError when D=1
+  end;
+end;
+
+procedure TDigitSetEditorForm.SetOriginalDigitsPossible(ASet: TDigitSet);
+var
+  D: TDigits;
+begin
+  if FOriginalDigitsPossible = ASet then Exit;
+  FOriginalDigitsPossible := ASet;
+  for D in TDigits do
+  begin
+    DigitCG.CheckEnabled[D-1] := (D in ASet);  //don't use Pred(D) here, gives RangeCheckError when D=1
   end;
 end;
 
@@ -91,5 +117,10 @@ begin
   Left := FPreferredRight - Width;
 end;
 
+procedure TDigitSetEditorForm.UpdateButtonState;
+begin
+  btnOk.Enabled := (GetCurrentDigitSet <> []);
+end;
+
 end.
 
diff --git a/applications/sudoku/scratchpad.pas b/applications/sudoku/scratchpad.pas
index f3512e18f..f7e413940 100644
--- a/applications/sudoku/scratchpad.pas
+++ b/applications/sudoku/scratchpad.pas
@@ -226,16 +226,17 @@ end;
 procedure TScratchForm.EditCell(ACol, ARow: Integer);
 var
   S: String;
-  DigitSet: TDigitSet;
+  CurrentDigitSet: TDigitSet;
 begin
   S := ScratchGrid.Cells[ACol, ARow];
-  DigitSet := StrToDigitSet(S);
-  DigitSetEditorForm.DigitSet := DigitSet;
+  CurrentDigitSet := StrToDigitSet(S);
+  DigitSetEditorForm.OriginalDigitsPossible := FRawData[ACol+1,ARow+1].DigitsPossible; //always set this first
+  DigitSetEditorForm.CurrentDigitSet := CurrentDigitSet;
   DigitSetEditorForm.Top := Top;
   DigitSetEditorForm.PreferredRight := Left;
   if (DigitSetEditorForm.ShowModal = mrOK) then
   begin
-    S := DigitSetToStr(DigitSetEditorForm.DigitSet);
+    S := DigitSetToStr(DigitSetEditorForm.CurrentDigitSet);
     ScratchGrid.Cells[ACol, ARow] := S;
   end;
 end;