diff --git a/ora/xlsx_builder_pkg.pkb b/ora/xlsx_builder_pkg.pkb
index 892ad3e..4811b24 100755
--- a/ora/xlsx_builder_pkg.pkb
+++ b/ora/xlsx_builder_pkg.pkb
@@ -1624,9 +1624,9 @@ ts timestamp := systimestamp;
       loop
         t_xxx := t_xxx || '<autoFilter ref="' ||
             alfan_col( nvl( workbook.sheets( s ).autofilters( a ).column_start, t_col_min ) ) ||
-            nvl( workbook.sheets( s ).autofilters( a ).row_start, workbook.sheets( s ).rows.first() ) || ':' ||
+            to_char( nvl( workbook.sheets( s ).autofilters( a ).row_start, workbook.sheets( s ).rows.first() )) || ':' ||
             alfan_col( coalesce( workbook.sheets( s ).autofilters( a ).column_end, workbook.sheets( s ).autofilters( a ).column_start, t_col_max ) ) ||
-            nvl( workbook.sheets( s ).autofilters( a ).row_end, workbook.sheets( s ).rows.last() ) || '"/>';
+            to_char( nvl( workbook.sheets( s ).autofilters( a ).row_end, workbook.sheets( s ).rows.last() )) || '"/>';
       end loop;
       if workbook.sheets( s ).mergecells.count() > 0
       then