diff --git modules/taxonomy/taxonomy.api.php modules/taxonomy/taxonomy.api.php
index 1527e48..4b50a5e 100644
--- modules/taxonomy/taxonomy.api.php
+++ modules/taxonomy/taxonomy.api.php
@@ -77,11 +77,11 @@ function hook_taxonomy_vocabulary_update($vocabulary) {
  * vocabularies from the database.
  *
  * @param $vocabulary
- *   A taxonomy vocabulary object.
+ *   A taxonomy vocabulary array.
  */
 function hook_taxonomy_vocabulary_delete($vocabulary) {
-  if (variable_get('taxonomy_' . $vocabulary->vid . '_synonyms', FALSE)) {
-    variable_del('taxonomy_' . $vocabulary->vid . '_synonyms');
+  if (variable_get('taxonomy_' . $vocabulary['vid'] . '_synonyms', FALSE)) {
+    variable_del('taxonomy_' . $vocabulary['vid'] . '_synonyms');
   }
 }