The Posix manpage says strcasecmp() is declared in and this indeed required for AIX 4.3 and xlc. diff -ur -N xpdf-3.04.orig/xpdf/GlobalParams.cc xpdf-3.04/xpdf/GlobalParams.cc --- xpdf-3.04.orig/xpdf/GlobalParams.cc 2014-05-30 19:29:23.000000000 +0200 +++ xpdf-3.04/xpdf/GlobalParams.cc 2014-05-30 19:47:44.000000000 +0200 @@ -54,6 +54,8 @@ #ifdef _WIN32 # define strcasecmp stricmp # define strncasecmp strnicmp +#else +# include #endif #if MULTITHREADED