As the automake documentation says: AM_CPPFLAGS: The contents of this variable are passed to every compilation that invokes the C preprocessor; it is a list of arguments to the preprocessor. For instance, -I and -D options should be listed here AM_CFLAGS: This is the variable the Makefile.am author can use to pass in additional C compiler flags. Javier Jard?n (1): src/Makefile: Use AM_CPPFLAGS instead AM_CFLAGS for preprocessor arguments src/Makefile.am | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) -- 1.8.1.4