In git versions > 1.8.4, the output ofgit status has changed such that the lines no longer have a "#" comment prefix by default. (See status.displayCommentPrefix inhttp://git-scm.com/docs/git-config) As a result, Repo.untracked_files() no longer parses the lines correctly. It seems that the --porcelain option togit status is specifically designed for this type of use.