automake mistaken source type

[D. Stimits]

I have defined in the project root configure.in:
AC_PROG_CXX

The structure of this simple project (it has essentially "hello world"
apps for a client subproject and a server subproject, that are otherwise
not doing anything) is as follows:
|-- AUTHORS
|-- COPYING
|-- ChangeLog
|-- INSTALL
|-- Makefile.am
|-- Makefile.in
|-- NEWS
|-- README
|-- acinclude.m4
|-- aclocal.m4
|-- bin
|-- clean
|-- config
|-- config.cache
|-- config.h
|-- config.h.in
|-- config.log
|-- config.status
|-- configure
|-- configure.in
|-- configure.scan
|-- doc
|-- etc
|-- install-sh
|-- lib
|-- missing
|-- mkinstalldirs
|-- src
|   |-- Makefile.am
|   |-- Makefile.in
|   |-- client
|   |   |-- Makefile.am
|   |   |-- Makefile.in
|   |   |-- client.h
|   |   `-- main.cxx
|   |-- include
|   |-- server
|   |   |-- Makefile.am
|   |   |-- Makefile.in
|   |   |-- main.cxx
|   |   `-- server.h
|   |-- stamp-h
|   `-- stamp-h.in
|-- stamp-h
|-- stamp-h.in
`-- test


Despite this being a C++ project, I am always getting (via "automake"
after "aclocal" and "autoconf" in the project root):
automake: Makefile.am: C source seen but `CC' not defined in
`configure.in'

No matter what I do, I can't get it to understand this is C++, not C.
Why would the AC_PROG_CXX be ignored? Are the .h files forcing this to
be considered C instead of C++?

D. Stimits, address@hidden