diff --git a/treeable/treeable.module b/treeable/treeable.module
index f45f472..e25c641 100644
--- a/treeable/treeable.module
+++ b/treeable/treeable.module
@@ -159,7 +159,7 @@ function treeable_form_field_ui_field_edit_form_alter(&$form, $form_state) {
   );
 
   if (field_behaviors_widget('multiple values', $instance) != FIELD_BEHAVIOR_DEFAULT) {
-    $form['instance']['widget']['settings']['treeable']['#description'] += '<br/>' . t('The currently active widget handles multiple value by itself. The hierarchical edit form cannot be enabled.');
+    $form['instance']['widget']['settings']['treeable']['#description'] .= '<br/>' . t('The currently active widget handles multiple value by itself. The hierarchical edit form cannot be enabled.');
     $form['instance']['widget']['settings']['treeable']['#value'] = 0;
     $form['instance']['widget']['settings']['treeable']['#disabled'] = TRUE;
   }