diff --git a/components/fpspreadsheet/examples/excel5demo/excel5write.lpr b/components/fpspreadsheet/examples/excel5demo/excel5write.lpr
index fe6d1e1e0..d896159de 100644
--- a/components/fpspreadsheet/examples/excel5demo/excel5write.lpr
+++ b/components/fpspreadsheet/examples/excel5demo/excel5write.lpr
@@ -314,14 +314,14 @@ begin
   MyWorksheet.WriteNumberFormat(r, 1, nfCustom, UTF8ToAnsi(fmt));
   MyWorksheet.WriteNumber(r, 2, -number);
   MyWorksheet.WriteNumberFormat(r, 2, nfCustom, UTF8ToAnsi(fmt));
-  inc(r);
+  inc(r);          {  --- not working correctly: Except reports an error
   fmt := '[Green]"¥"#,##0.0_);[Red]-"¥"#,##0.0';
   MyWorksheet.WriteUTF8Text(r, 0, 'nfCustom, '+fmt);
   MyWorksheet.WriteNumber(r, 1, number);
   MyWorksheet.WriteNumberFormat(r, 1, nfCustom, UTF8ToAnsi(fmt));
   MyWorksheet.WriteNumber(r, 2, -number);
   MyWorksheet.WriteNumberFormat(r, 2, nfCustom, UTF8ToAnsi(fmt));
-  inc(r);
+  inc(r);            }
   MyWorksheet.WriteUTF8Text(r, 0, 'nfCustom, _("$"* #,##0_);_("$"* (#,##0);_("$"* "-"_);_(@_)');
   MyWorksheet.WriteNumber(r, 1, number);
   MyWorksheet.WriteNumberFormat(r, 1, nfCustom, '_("$"* #,##0_);_("$"* (#,##0);_("$"* "-"_);_(@_)');
@@ -356,7 +356,6 @@ begin
   MyWorksheet.WriteUTF8Text(r, 0, 'nfTimeInterval, h');
   MyWorksheet.WriteDateTime(r, 1, number, nfTimeInterval, 'h');
 
-
   //MyFormula.FormulaStr := '';
 
   // Creates a new worksheet
diff --git a/components/fpspreadsheet/fpspreadsheet.pas b/components/fpspreadsheet/fpspreadsheet.pas
index 455a6fb9b..9a1a5b6fa 100755
--- a/components/fpspreadsheet/fpspreadsheet.pas
+++ b/components/fpspreadsheet/fpspreadsheet.pas
@@ -2129,7 +2129,10 @@ begin
     // The user can choose another date format if he wants to
 
     if AFormatStr = '' then
-      AFormatStr := BuildDateTimeFormatString(AFormat, Workbook.FormatSettings, AFormatStr);
+      AFormatStr := BuildDateTimeFormatString(AFormat, Workbook.FormatSettings, AFormatStr)
+    else
+    if AFormat = nfTimeInterval then
+      AFormatStr := AddIntervalBrackets(AFormatStr);
 
     // Check whether the formatstring is for date/times.
     if AFormatStr <> '' then begin