diff --git a/components/fpspreadsheet/examples/other/conditional_formatting/demo_conditional_formatting.pas b/components/fpspreadsheet/examples/other/conditional_formatting/demo_conditional_formatting.pas
index 067050c53..8fd4d1f61 100644
--- a/components/fpspreadsheet/examples/other/conditional_formatting/demo_conditional_formatting.pas
+++ b/components/fpspreadsheet/examples/other/conditional_formatting/demo_conditional_formatting.pas
@@ -85,6 +85,16 @@ begin
     fmtIdx := wb.AddCellFormat(fmt);
     sh.WriteConditionalCellFormat(Range(0, 0, 100, 100), cfcContainsErrors, fmtIdx);
 
+
+    { ------ 6th conditional format: unique/duplicate values ----------------- }
+    sh.WriteNumber(0, 1, 1.0);
+    sh.WriteNumber(1, 1, 99.0);
+    InitFormatRecord(fmt);
+    fmt.SetBackgroundColor(scSilver);
+    sh.WriteConditionalCellFormat(Range(0, 0, 1, 1), cfcUnique, wb.AddCellFormat(fmt));
+    fmt.SetBackgroundColor(scGreen);
+    sh.WriteConditionalCellFormat(Range(0, 0, 1, 1), cfcDuplicate, wb.AddCellFormat(fmt));
+
     { ------ Save workbook to file-------------------------------------------- }
     wb.WriteToFile('test.xlsx', true);
   finally
diff --git a/components/fpspreadsheet/source/common/xlsxooxml.pas b/components/fpspreadsheet/source/common/xlsxooxml.pas
index c8903d7c3..8181fd210 100644
--- a/components/fpspreadsheet/source/common/xlsxooxml.pas
+++ b/components/fpspreadsheet/source/common/xlsxooxml.pas
@@ -3360,7 +3360,7 @@ const
 var
   i: Integer;
   dxfID: Integer;
-  aveStr, stdDevStr, eqAveStr, opStr: String;
+  typeStr, aveStr, stdDevStr, eqAveStr, opStr: String;
   firstCellOfRange: String;
 begin
   dxfID := -1;
@@ -3424,6 +3424,16 @@ begin
           opStr
         ]));
       end;
+
+    cfcDuplicate, cfcUnique:
+      begin
+        if ARule.Condition = cfcUnique then
+          typeStr := 'uniqueValues'
+        else
+          typeStr := 'duplicateValues';
+        AppendToStream(AStream, Format(
+          '<cfRule type="%s" dxfId="%d" priority="%d" />', [typeStr, dxfID, APriority]));
+      end;
   else
     FWorkbook.AddErrorMsg('ConditionalFormat operator not supported.');
   end;