diff -u b/core/modules/forum/forum.install b/core/modules/forum/forum.install
--- b/core/modules/forum/forum.install
+++ b/core/modules/forum/forum.install
@@ -31,8 +31,7 @@
   field_associate_fields('taxonomy');
   // Create the forum vocabulary if it does not exist.
   $config = config('forum.settings');
-  $vid = $config->get('vocabulary');
-  $vocabulary = taxonomy_vocabulary_load($vid);
+  $vocabulary = taxonomy_vocabulary_machine_name_load($config->get('vocabulary'));
   if (!$vocabulary) {
     $vocabulary = entity_create('taxonomy_vocabulary', array(
       'name' => t('Forums'),