Is there a way to prevent duplicate taxonomy terms in Drupal (7)?

I'm using a 开发者_JS百科free-tagging system in Drupal and am running into a problem: if I re-use a taxonomy term, it is added (redundantly) to the taxonomy vocabulary. Is there a way to limit a vocabulary to distinct terms?

here is the module for this.

http://drupal.org/project/taxonomy_dupecheck

hope that helps

By default, vocabularies which are "free tagging" in Drupal do not add redundant terms if one already exists in the given vocabulary. Are you certain the terms are spelled absolutely identically? Are you using any other modules that might affect taxonomy?