The Posix manpage says strcasecmp() is declared in and this indeed required for AIX 4.3 and xlc. diff -ur -N xpdf-3.03.orig/xpdf/GlobalParams.cc xpdf-3.03/xpdf/GlobalParams.cc --- xpdf-3.03.orig/xpdf/GlobalParams.cc 2012-10-19 10:01:03.000000000 +0200 +++ xpdf-3.03/xpdf/GlobalParams.cc 2012-10-19 10:06:40.000000000 +0200 @@ -48,6 +48,8 @@ #ifdef WIN32 # define strcasecmp stricmp +#else +# include #endif #if MULTITHREADED