diff --git a/htdocs/core/modules/export/export_excel.modules.php b/htdocs/core/modules/export/export_excel.modules.php
index 9d89d53de2a..43cb4d6e9cd 100644
--- a/htdocs/core/modules/export/export_excel.modules.php
+++ b/htdocs/core/modules/export/export_excel.modules.php
@@ -510,6 +510,7 @@ class ExportExcel extends ModeleExports
     {
 
         $c = intval($c);
+        $letter = '';
         if ($c <= 0) {
             return '';
         }