diff --git a/mod/data/field/checkbox/field.class.php b/mod/data/field/checkbox/field.class.php
index 6c53fc6..b70bd4e 100755
--- a/mod/data/field/checkbox/field.class.php
+++ b/mod/data/field/checkbox/field.class.php
@@ -51,6 +51,7 @@ class data_field_checkbox extends data_field_base {
             if ($checkbox === '') {
                 continue; // skip empty lines
             }
+            $str .= '<input type="hidden" name="field_' . $this->field->id . '[]" value="" />';
             $str .= '<input type="checkbox" id="field_'.$this->field->id.'_'.$i.'" name="field_' . $this->field->id . '[]" ';
             $str .= 'value="' . s($checkbox) . '" ';