You generally need a compiler other than Gcc (GNU Compiler) 2.96. Gcc 2.96 has a bug in its inlining optimization. It generates incorrect code. Netpbm source code takes advantage of inlining and you normally build Netpbm with inlining enabled. Therefore, if you use Gcc 2.96 you will get broken Netpbm programs. The usual symptom is bogus syntax error messages when you run the program. You can avoid this compiler bug by using a -O0 compile option instead of the usual -O3. The automatic configuration program will usually detect that you need this and set it up for you. This will make some programs noticeably slower, though.