The Follwing packages are installed on my AIX 6.1 box gcc-4.7.2-1 gcc-c++-4.7.2-1 gcc-cpp-4.7.2-1 gcc-gfortran-4.7.2-1 libgcc-4.7.2-1 libgomp-4.7.2-1 libstdc++-4.7.2-1 libstdc++-devel-4.7.2-1 gmp-5.0.5-1 libmpc-1.0.1-2 libmpc-devel-1.0.1-2 libmpcdec-1.2.6-1 libmpcdec-devel-1.2.6-1 mpfr-3.1.1-1 mpfr-devel-3.1.1-1 flex-2.5.4a-6 m4-1.4.1-1 bison-1.875-3 libiconv-1.14-2 gettext-0.17-1 gettext-devel-0.17-1 I used follwing command to confiure the apache: ./configure CC="gcc -maix64" CFLAGS="-maix64" CXX="gcc -maix64" CPPFLAGS="-maix64" NM="nm -X64" AR="ar -X64" LDFLAGS="-L/usr/ccs/bin/ld" --prefix=/usr/local/share/bld/apache2 --enable-ssl=shared --with-ssl=/usr/local/share/bld/ssl --enable-deflate=shared --with-z=/usr/local/share/bld/zlib --enable-mods-shared=all --with-expat=builtin --with-pcre=/usr/local/share/bld/pcre --with-included-apr --enable-v4-mapped The above command executed successfully. While executing the make command follwing error is reported: bison -pap_expr_yy --defines=/usr/local/share/bld/httpd-2.4.3/server/util_expr_parse.h -o /usr/local/share/bld/httpd-2.4.3/server/util_expr_parse.c /usr/local/share/bld/httpd-2.4.3/server/util_expr_parse.y /usr/local/share/bld/httpd-2.4.3/server/util_expr_parse.y:28.1: invalid character: `%' /usr/local/share/bld/httpd-2.4.3/server/util_expr_parse.y:28.2-4: parse error, unexpected "identifier" make: 1254-004 The error code from the last command is 1.