-dnl libxml2 is used by the hivex library.
-PKG_CHECK_MODULES([LIBXML2], [libxml-2.0])
-AC_SUBST([LIBXML2_CFLAGS])
-AC_SUBST([LIBXML2_LIBS])
+dnl hivex library (highly recommended).
+dnl This used to be a part of libguestfs, but was spun off into its
+dnl own separate upstream project in libguestfs 1.0.85.
+HAVE_HIVEX=yes
+PKG_CHECK_MODULES([HIVEX], [hivex],,[
+ HAVE_HIVEX=no
+ AC_MSG_WARN([Hivex library and headers are missing, so optional Windows Registry tools won't be built])])
+AM_CONDITIONAL([HAVE_HIVEX],[test "x$HAVE_HIVEX" = "xyes"])
+AC_SUBST([HIVEX_CFLAGS])
+AC_SUBST([HIVEX_LIBS])