diff --git a/Source/Layout/Markdown4D.Editor.Model.pas b/Source/Layout/Markdown4D.Editor.Model.pas
index f300c21..d02dada 100644
--- a/Source/Layout/Markdown4D.Editor.Model.pas
+++ b/Source/Layout/Markdown4D.Editor.Model.pas
@@ -88,6 +88,7 @@   TMarkdownEditorModel = class
     function CollapsedIndexOf(const HeaderOffset: Integer): Integer;
     function TryRegionAtHeader(const HeaderLine: Integer; out Region: TFoldRegion): Boolean;
     procedure WrapOrToggle(const Marker: string);
+    function MarkersSurroundSelection(const Start, Len: Integer; const Marker: string): Boolean;
     procedure InsertLink;
     procedure WrapCodeBlock;
     procedure ToggleHeading(const Level: Integer);
@@ -1313,12 +1314,55 @@ procedure TMarkdownEditorModel.WrapOrToggle(const Marker: string);
     Exit;
   end;
 
+  // Wrapping leaves the selection on the word itself, inside the markers it just
+  // added, so pressing the same command again has to recognise them from there.
+  // Without this a second press wraps the wrapped text and doubles the markers.
+  if MarkersSurroundSelection(Start, Len, Marker) then
+  begin
+    ApplyReplace(Start - MarkerLen, Len + 2 * MarkerLen, Selected, False);
+    FAnchor := Start - MarkerLen;
+    FCaret := FAnchor + System.Length(Selected);
+    Exit;
+  end;
+
   const Wrapped = Marker + Selected + Marker;
   ApplyReplace(Start, Len, Wrapped, False);
   FAnchor := Start + MarkerLen;
   FCaret := Start + MarkerLen + System.Length(Selected);
 end;
 
+function TMarkdownEditorModel.MarkersSurroundSelection(const Start, Len: Integer;
+  const Marker: string): Boolean;
+begin
+  Result := False;
+
+  const MarkerLen = System.Length(Marker);
+  const LeadingStart = Start - MarkerLen + 1;
+  const TrailingStart = Start + Len + 1;
+
+  if (LeadingStart < 1) or (TrailingStart + MarkerLen - 1 > System.Length(FText)) then
+    Exit;
+
+  if Copy(FText, LeadingStart, MarkerLen) <> Marker then
+    Exit;
+  if Copy(FText, TrailingStart, MarkerLen) <> Marker then
+    Exit;
+
+  // A marker that continues into more of the same character belongs to a longer
+  // run, and so to a different construct: the single asterisks either side of a
+  // word inside '**bold**' are the bold, not an italic to be taken away.
+  const MarkerChar = Marker[1];
+
+  if (LeadingStart > 1) and (FText[LeadingStart - 1] = MarkerChar) then
+    Exit;
+
+  const AfterTrailing = TrailingStart + MarkerLen;
+  if (AfterTrailing <= System.Length(FText)) and (FText[AfterTrailing] = MarkerChar) then
+    Exit;
+
+  Result := True;
+end;
+
 procedure TMarkdownEditorModel.InsertLink;
 begin
   const Start = SelectionStart;
diff --git a/Tests/Markdown4D.Editor.Model.Tests.pas b/Tests/Markdown4D.Editor.Model.Tests.pas
index 7d00b49..84fdc42 100644
--- a/Tests/Markdown4D.Editor.Model.Tests.pas
+++ b/Tests/Markdown4D.Editor.Model.Tests.pas
@@ -166,6 +166,15 @@   TMarkdownEditorModelTests = class
     [TestCase('On bold selection unwraps', '**Hello** world,9,Hello world')]
     procedure ExecuteBold_Various_TogglesBoldMarkers(const Text: string; const SelectionEnd: Integer; const Expected: string);
 
+    [Test]
+    procedure ExecuteBold_Twice_LeavesTheWordUnchanged;
+
+    [Test]
+    procedure ExecuteBold_MarkersJustOutsideSelection_RemovesThem;
+
+    [Test]
+    procedure ExecuteItalic_OnABoldWord_AddsItalicRatherThanEatingTheBold;
+
     [Test]
     procedure ExecuteLink_InsertsPlaceholderWithCaretInUrl;
 
@@ -764,6 +773,43 @@ procedure TMarkdownEditorModelTests.ExecuteBold_Various_TogglesBoldMarkers(const
   Assert.AreEqual(Expected, FModel.Text);
 end;
 
+procedure TMarkdownEditorModelTests.ExecuteBold_Twice_LeavesTheWordUnchanged;
+begin
+  // What a user actually does: select a word, press Bold, press Bold again. The
+  // first press leaves the selection on the word itself, inside the markers it
+  // just added, so the second press has to recognise them from there.
+  FModel.LoadText('Unidentified');
+  FModel.SetSelection(0, 12);
+
+  FModel.ExecuteCommand(TEditorCommand.Bold);
+  Assert.AreEqual('**Unidentified**', FModel.Text, 'after the first press');
+
+  FModel.ExecuteCommand(TEditorCommand.Bold);
+  Assert.AreEqual('Unidentified', FModel.Text, 'after the second press');
+end;
+
+procedure TMarkdownEditorModelTests.ExecuteBold_MarkersJustOutsideSelection_RemovesThem;
+begin
+  FModel.LoadText('a **word** b');
+  FModel.SetSelection(4, 4);
+
+  FModel.ExecuteCommand(TEditorCommand.Bold);
+
+  Assert.AreEqual('a word b', FModel.Text);
+end;
+
+procedure TMarkdownEditorModelTests.ExecuteItalic_OnABoldWord_AddsItalicRatherThanEatingTheBold;
+begin
+  // The single asterisks around the selection belong to a bold run, not to an
+  // italic one, so italic has to add its own rather than strip half the bold.
+  FModel.LoadText('**word**');
+  FModel.SetSelection(2, 4);
+
+  FModel.ExecuteCommand(TEditorCommand.Italic);
+
+  Assert.AreEqual('***word***', FModel.Text);
+end;
+
 procedure TMarkdownEditorModelTests.ExecuteLink_InsertsPlaceholderWithCaretInUrl;
 begin
   FModel.LoadText('Hello');