I just discovered that perhaps ntpath.join should be even more clever. Windows supports current directories for every drive separately, so perhaps ntpath.join('c:/x', 'd:/y', 'c:z') should return 'c:/x\\z', not 'c:/z'. Could anyone please check it? Create directory x/z on drive c: and directory y on drive d:, then execute following commands: cd c:/x cd d:/y cd c:z What is resulting current working directory? Here is a patch which implements this algorithm.