iconv generates spurious warnings when unconvertible sequences are encountered while IGNORE is enabled. Expected behavior (from libiconv-1.14): ezyang@javelin:~/Dev/glibc/build$ printf "\xc3\xbc\x73" | ~/Desktop/libiconv-1.14/src/iconv_no_i18n -f utf-8 -t ascii//IGNORE s Actual behavior (from latest Git glibc-2.14-567-ga4647e7): ezyang@javelin:~/Dev/glibc/build$ printf "\xc3\xbc\x73" | ./testrun.sh iconv/iconv_prog -f utf-8 -t ascii//IGNORE siconv/iconv_prog: illegal input sequence at position 5
You have to use the -c option for iconv and not //IGNORE.