diff --git a/htdocs/core/class/html.form.class.php b/htdocs/core/class/html.form.class.php
index b701d06d721..251c65c80c0 100644
--- a/htdocs/core/class/html.form.class.php
+++ b/htdocs/core/class/html.form.class.php
@@ -2219,6 +2219,7 @@ class Form
         {
             $autoOpen=true;
             $dialogconfirm='dialog-confirm';
+            $button='';
             if (! is_int($useajax))
             {
                 $button=$useajax;