diff --git a/components/fpspreadsheet/xlsbiff8.pas b/components/fpspreadsheet/xlsbiff8.pas
index e7a4463ef..f5781c101 100755
--- a/components/fpspreadsheet/xlsbiff8.pas
+++ b/components/fpspreadsheet/xlsbiff8.pas
@@ -125,6 +125,7 @@ type
       const AValue: string; ACell: PCell); override;
     procedure WriteRPNFormula(AStream: TStream; const ARow, ACol: Cardinal;
       const AFormula: TsRPNFormula; ACell: PCell); override;
+    function WriteString_8bitLen(AStream: TStream; AString: String): Integer; override;
     procedure WriteStringRecord(AStream: TStream; AString: string);
     procedure WriteStyle(AStream: TStream);
     procedure WriteWindow2(AStream: TStream; ASheet: TsWorksheet);
@@ -927,12 +928,16 @@ begin
     INT_EXCEL_TOKEN_TSTR: { fekString }
     begin
       // string constant is stored as widestring in BIFF8
+      // Writing is done by the virtual method WriteString_8bitLen.
+      Inc(RPNLength, WriteString_8bitLen(AStream, AFormula[i].StringValue));
+      {
       wideStr := UTF8Decode(AFormula[i].StringValue);
       len := Length(wideStr);
       AStream.WriteByte(len); // char count in 1 byte
       AStream.WriteByte(1);   // Widestring flags, 1=regular unicode LE string
       AStream.WriteBuffer(WideStringToLE(wideStr)[1], len * Sizeof(WideChar));
       Inc(RPNLength, 1 + 1 + len*SizeOf(WideChar));
+      }
     end;
 
     INT_EXCEL_TOKEN_TBOOL:  { fekBool }
@@ -990,6 +995,24 @@ begin
     WriteStringRecord(AStream, ACell^.UTF8StringValue);
 end;
 
+{ Helper function for writing a string with 8-bit length. Overridden version
+  for BIFF8. Called for writing rpn formula string tokens.
+  Returns the count of bytes written}
+function TsSpreadBIFF8Writer.WriteString_8BitLen(AStream: TStream;
+  AString: String): Integer;
+var
+  len: Integer;
+  wideStr: WideString;
+begin
+  // string constant is stored as widestring in BIFF8
+  wideStr := UTF8Decode(AString);
+  len := Length(wideStr);
+  AStream.WriteByte(len); // char count in 1 byte
+  AStream.WriteByte(1);   // Widestring flags, 1=regular unicode LE string
+  AStream.WriteBuffer(WideStringToLE(wideStr)[1], len * Sizeof(WideChar));
+  Result := 1 + 1 + len * SizeOf(WideChar);
+end;
+
 procedure TsSpreadBIFF8Writer.WriteStringRecord(AStream: TStream;
   AString: String);
 var
diff --git a/components/fpspreadsheet/xlscommon.pas b/components/fpspreadsheet/xlscommon.pas
index b81468d8f..8343bb41d 100644
--- a/components/fpspreadsheet/xlscommon.pas
+++ b/components/fpspreadsheet/xlscommon.pas
@@ -448,6 +448,8 @@ type
     procedure GetLastColCallback(ACell: PCell; AStream: TStream);
     function GetLastColIndex(AWorksheet: TsWorksheet): Word;
     function FormulaElementKindToExcelTokenID(AElementKind: TFEKind; out ASecondaryID: Word): Word;
+    // Helper function for writing a string with 8-bit length }
+    function WriteString_8BitLen(AStream: TStream; AString: String): Integer; virtual;
 
     // Write out BLANK cell record
     procedure WriteBlank(AStream: TStream; const ARow, ACol: Cardinal;
@@ -2141,6 +2143,23 @@ begin
   AStream.WriteWord(WordToLE(flags));
 end;
 
+{ Helper function for writing a string with 8-bit length. Here, we implement the
+  version for ansistrings since it is valid for all BIFF versions except BIFF8
+  where it has to overridden. Is called for writing a string rpn token.
+  Returns the count of bytes written. }
+function TsSpreadBIFFWriter.WriteString_8bitLen(AStream: TStream;
+  AString: String): Integer;
+var
+  len: Byte;
+  s: ansistring;
+begin
+  s := AString;
+  len := Length(s);
+  AStream.WriteByte(len);
+  AStream.WriteBuffer(s[1], len);
+  Result := 1 + len;
+end;
+
 { Writes an Excel 5/8 WINDOW1 record
   This record contains general settings for the document window and
   global workbook settings.