Hi all, I am totally new with auto tools :-) When trying to make a very first project, I do encounter always the same issue with _CXX_COMPILE_STDCXX macro. Below the current content of both configure.ac and Makefile.am $ configure.ac AC_CONFIG_MACRO_DIRS([m4]) m4_pattern_allow([AC_PROG_CC_C99]) m4_include([m4/ax_check_compile_flag.m4]) m4_include([m4/ax_cxx_compile_stdcxx.m4]) m4_include([m4/ax_cxx_compile_stdcxx_11.m4]) AC_CONFIG_SRCDIR(configure.ac) AM_CONFIG_HEADER(config.h) AM_INIT_AUTOMAKE AC_PROG_CC AX_CHECK_COMPILE_FLAG([-std=gnu11], [CFLAGS+=" -std=gnu11"], [AC_PROG_CC_C99]) AC_PROG_CXX AX_CXX_COMPILE_STDCXX_11([ext], [optional]) AC_PROG_LIBTOOL AC_CONFIG_FILES(Makefile) AC_OUTPUT $ cat Makefile.am ACLOCAL_AMFLAGS = ${ACLOCAL_FLAGS} -I m4 bin_PROGRAMS = test test_SOURCES = test.cc $ ls -l m4 ax_check_compile_flag.m4 ax_check_openssl.m4 ax_cxx_compile_stdcxx.m4 ax_cxx_compile_stdcxx_11.m4 libtool.m4 lt~obsolete.m4 ltoptions.m4 ltsugar.m4 ltversion.m4 Following commands seem to be OK ... aclocal autoreconf --force --install automake --add-missing BUT when doing the configure script .... I get the same error ... $ ./configure ./configure: line 2428: syntax error near unexpected token `AX_CXX_COMPILE_STDCXX' ./configure: line 2428: `AX_REQUIRE_DEFINED(AX_CXX_COMPILE_STDCXX)' Thanks in advance for your help :-) Best Regards, Vincent