diff --git a/components/fpspreadsheet/source/common/fpstypes.pas b/components/fpspreadsheet/source/common/fpstypes.pas
index 4798accd5..559145391 100644
--- a/components/fpspreadsheet/source/common/fpstypes.pas
+++ b/components/fpspreadsheet/source/common/fpstypes.pas
@@ -168,7 +168,7 @@ const
   STR_ERR_ARG_ERROR = '#N/A';
   // No Excel errors
   STR_ERR_FORMULA_NOT_SUPPORTED= '<FMLA?>';
-  STR_ERR_UNKNOWN = '#UNKNWON!';
+  STR_ERR_UNKNOWN = '#UNKNOWN!';
 
   {@@ Maximum count of worksheet columns}
   MAX_COL_COUNT = 65535;
@@ -193,6 +193,10 @@ const
       unique value simplifies many things... }
   FPS_LINE_ENDING = #10;
 
+  {@@ Replacement character used in broken UTF8 strings. Alternate replacement
+      chars could be: #$E2#$8E#$95 = box, or #$EF#$BF#$BD = "unicode replacement character" }
+  FPS_REPLACEMENT_CHAR = '?';
+
 var
   CSVParams: TsCSVParams = (
     SheetIndex: 0;
diff --git a/components/fpspreadsheet/source/common/fpsutils.pas b/components/fpspreadsheet/source/common/fpsutils.pas
index a4da2ad6a..073c26d84 100644
--- a/components/fpspreadsheet/source/common/fpsutils.pas
+++ b/components/fpspreadsheet/source/common/fpsutils.pas
@@ -241,8 +241,8 @@ function GetFontAsString(AFont: TsFont): String;
 
 function ISO8601StrToDateTime(s: String): TDateTime;
 
-function UTF8CodePoints(AText: string; out sa: TStringArray; AReplacement: String = #$E2#$8E#$95): Boolean;
-function ValidUTF8Text(var AText: String; AReplacement: String = #$E2#$8E#$95): Boolean;
+function UTF8CodePoints(AText: string; out sa: TStringArray): Boolean;
+function ValidUTF8Text(var AText: String): Boolean;
 
 procedure AppendToStream(AStream: TStream; const AString: String); inline; overload;
 procedure AppendToStream(AStream: TStream; const AString1, AString2: String); inline; overload;
@@ -3222,8 +3222,7 @@ end;
   returns them as an array of string (sa). The result of the function is
   false if at least one codepoint is broken UTF8.
 -------------------------------------------------------------------------------}
-function UTF8CodePoints(AText: String; out sa: TStringArray;
-  AReplacement: string = #$E2#$8E#$95): Boolean;
+function UTF8CodePoints(AText: String; out sa: TStringArray): Boolean;
 var
   n: Integer;
   ch: String;
@@ -3245,7 +3244,7 @@ begin
     chLen := UTF8CodePointSize(P);
     if (chLen = 1) and (P^ > #127) then
     begin
-      ch := AReplacement;
+      ch := FPS_REPLACEMENT_CHAR;
       Result := false;
     end else
     begin
@@ -3259,7 +3258,7 @@ begin
   SetLength(sa, n);
 end;
 
-function ValidUTF8Text(var AText: string; AReplacement: String = #$E2#$8E#$95): Boolean;
+function ValidUTF8Text(var AText: string): Boolean;
 var
   i: Integer;
   P: PChar;
@@ -3271,7 +3270,7 @@ begin
     if i >= 0 then
     begin
       Delete(AText, i+1, 1);
-      Insert(AReplacement, AText, i+1);
+      Insert(FPS_REPLACEMENT_CHAR, AText, i+1);
       Result := false;
     end;
   until (i < 0);
diff --git a/components/fpspreadsheet/source/common/fpsxmlcommon.pas b/components/fpspreadsheet/source/common/fpsxmlcommon.pas
index 42df28f21..92840120e 100644
--- a/components/fpspreadsheet/source/common/fpsxmlcommon.pas
+++ b/components/fpspreadsheet/source/common/fpsxmlcommon.pas
@@ -47,7 +47,7 @@ function GetNodeValue(ANode: TDOMNode): String;
 function LineEndingToBR(const AText: String): String;
 function UTF8TextToXMLText(AText: string; ProcessLineEndings: Boolean = false): string;
 function ValidXMLText(var AText: string; ReplaceSpecialChars: Boolean = true;
-  ProcessLineEndings: Boolean = false; InvalidUTF8Replacement: String = #$E2#$8E#$95): Boolean;
+  ProcessLineEndings: Boolean = false): Boolean;
 function XMLQuote(AText: String): String;
 
 procedure UnzipFile(AZipFileName, AZippedFile, ADestFolder: String);
@@ -202,25 +202,24 @@ end;
                                codes (e.g. '>' --> '&gt;')
   @param  ProcessLineEndings   If TRUE line ending characters are replaced by
                                their HTML entities.
-  @param  InvalidUTF8Replacement  UTF8-character inserted for a malformed UTF8 codepoint.
   @return FALSE if characters were replaced, TRUE otherwise.
 -------------------------------------------------------------------------------}
 function ValidXMLText(var AText: string;
   ReplaceSpecialChars: Boolean = true;
-  ProcessLineEndings: Boolean = false;
-  InvalidUTF8Replacement: String = #$E2#$8E#$95): Boolean;
+  ProcessLineEndings: Boolean = false): Boolean;
+// Alternate replacement chars: #$E2#$8E#$95 = box, or #$EF#$BF#$BD = "replacement character"
 var
   i: Integer;
 begin
   // Replace broken UTF8 codepoints
-  Result := ValidUTF8Text(AText, InvalidUTF8Replacement);
+  Result := ValidUTF8Text(AText);
 
   // Replace ASCII characters which are not allowed in XML.
   for i := Length(AText) downto 1 do
     if (AText[i] < #32) and not (AText[i] in [#9, #10, #13]) then begin
       // Replace invalid character by box symbol
       Delete(AText, i, 1);
-      Insert(InvalidUTF8Replacement, AText, i);
+      Insert(FPS_REPLACEMENT_CHAR, AText, i);
       Result := false;
     end;
 
diff --git a/components/fpspreadsheet/source/common/xlsbiff5.pas b/components/fpspreadsheet/source/common/xlsbiff5.pas
index f9d38e060..186327016 100644
--- a/components/fpspreadsheet/source/common/xlsbiff5.pas
+++ b/components/fpspreadsheet/source/common/xlsbiff5.pas
@@ -1876,7 +1876,7 @@ begin
     exit;
 
   lValue := FixLineEnding(AValue);     // This does not change indices for rtf.
-  if not ValidUTF8Text(lValue, '?') then
+  if not ValidUTF8Text(lValue) then
     Workbook.AddErrorMsg(
       rsInvalidCharacterInCell, [
       GetCellString(ARow, ACol)