Index: modules/rules_core.rules.inc
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/rules/modules/Attic/rules_core.rules.inc,v
retrieving revision 1.1.2.6
diff -u -p -r1.1.2.6 rules_core.rules.inc
--- modules/rules_core.rules.inc	16 Feb 2011 17:21:47 -0000	1.1.2.6
+++ modules/rules_core.rules.inc	21 Feb 2011 12:22:19 -0000
@@ -105,7 +105,11 @@ function rules_rules_core_data_info() {
       );
     }
   }
-  $return['taxonomy_vocabulary']['wrapper class'] = 'RulesTaxonomyVocabularyWrapper';
+
+  if (module_exists('taxonomy')) {
+    $return['taxonomy_vocabulary']['wrapper class'] = 'RulesTaxonomyVocabularyWrapper';
+  }
+
   return $return;
 }