AC_PROG_RANLIB
AC_PROG_LN_S
-AC_PATH_PROG([PATH_ASCIIDOC], [asciidoc])
+AC_PATH_PROG([PATH_ASCIIDOC], [asciidoc], [no])
+AS_IF([test x"$PATH_ASCIIDOC" = x"no"],
+ [AC_MSG_ERROR([asciidoc is required for generating man pages])])
AC_PATH_PROG([PATH_XMLTO], [xmlto], [no])
AS_IF([test x"$PATH_XMLTO" = x"no"],
[AC_MSG_ERROR([xmlto is required for generating man pages])])