Appartently the check at newlib/testsuite/newlib.wctype/twctype.c:40 is wrong since the unicode character 0x0967 is a number, not a letter. See https://www.fileformat.info/info/unicode/char/0967/index.htm The nearest letter I've found is 0x0961, see https://www.fileformat.info/info/unicode/char/0961/index.htm Giacomo