I was building gcc 4.4.3 on Red Hat Enterprise Linux Server release 6.3 (Santiago). Build has passed, however, fixedincludes directory is missing some headers which were present in the redhat5.5 installation. Has someone seen same behavior? Configure command is(in both redhat5.5 and redhat6.3): ../configure --prefix=/path/to/gcc/GCC_4.4.3_RH6.X --exec-prefix=/path/to/gcc/GCC_4.4.3_RH6.X/Linux --with-ppl=/path/to/gcc/GCC_4.4.3_RH6.X/Linux --with-gmp=/path/to/gcc/GCC_4.4.3_RH6.X/Linux --with-mpc=/path/to/gcc/GCC_4.4.3_RH6.X/Linux --with-mpfr=/path/to/gcc/GCC_4.4.3_RH6.X/Linux --with-mpfr-include=/path/to/gcc/GCC_4.4.3_RH6.X/include --with-cloog=/path/to/gcc/GCC_4.4.3_RH6.X/Linux --with-cloog-lib=/path/to/gcc/GCC_4.4.3_RH6.X/Linux/lib64 --with-ld=/path/to/gcc/GCC_4.4.3_RH6.X/Linux/bin/ld --with-as=/path/to/gcc/GCC_4.4.3_RH6.X/Linux/bin/as --enable-languages=c,c++ --enable-threads **5.5 installation:** /path/to/gcc/GCC_4.4.3/Linux/lib/gcc/x86_64-unknown-linux-gnu/4.4.3/include-fixed bits features.h limits.h net-snmp openssl schily sound sys wchar.h xorg zutil.h dhcp4client libdevmapper.h linux nss3 README slang speech_tools syslimits.h X11 xulrunner-sdk-1.9 **6.3 installation:** /path/to/gcc/GCC_4.4.3_RH6.X/Linux/lib/gcc/x86_64-unknown-linux-gnu/4.4.3/include-fixed limits.h linux net-snmp nss3 openssl README syslimits.h X11 It seems to me that because features.h is picked from the system header on Redhat6.x, when I compile my project source tree, not from the fixedincludes, as it is missing anyway, compilation is failing.