diff --git a/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_NETINET_IN6_H.h b/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_NETINET_IN6_H.h
index 0e898ed..0090c67 100644
--- a/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_NETINET_IN6_H.h
+++ b/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_NETINET_IN6_H.h
@@ -1,17 +1,10 @@
-// HAVE_NETINET_IN6_H : BUILD2_AUTOCONF_LIBC_VERSION
-
-#ifndef BUILD2_AUTOCONF_LIBC_VERSION
-#  error BUILD2_AUTOCONF_LIBC_VERSION appears to be conditionally included
-#endif
+// HAVE_NETINET_IN6_H
 
+/* Looks like netinet/in6.h only exists on System V-derived OSes like AIX,
+ * HP-UX, Solaris, and Illumos.
+ *
+ * On Linux the IPv6 constructs are defined in netinet/in.h and on FreeBSD,
+ * OpenBSD, NetBSD, and MacOS netinet/in.h includes netinet6/in6.h (note: not
+ * netinet/) so the latter should not be included directly.
+ */
 #undef HAVE_NETINET_IN6_H
-
-/* On Linux the IPv6 constructs are defined in netinet/in.h and on FreeBSD
- * netinet/in.h includes netinet6/in6.h (note: not netinet/) so the latter
- * should not be included directly.
-*/
-#if defined(__OpenBSD__) || \
-    defined(__NetBSD__)  || \
-    defined(BUILD2_AUTOCONF_MACOS)
-#  define HAVE_NETINET_IN6_H 1
-#endif
diff --git a/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_SYS_SENDFILE_H.h b/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_SYS_SENDFILE_H.h
index 7fc6cfe..dd04edc 100644
--- a/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_SYS_SENDFILE_H.h
+++ b/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_SYS_SENDFILE_H.h
@@ -6,10 +6,8 @@
 
 #undef HAVE_SYS_SENDFILE_H
 
-/* Since FreeBSD 3.0, Mac OS 10.5, glibc 2.1
+/* Since glibc 2.1.
  */
-#if BUILD2_AUTOCONF_FREEBSD_PREREQ(3, 0)   || \
-    BUILD2_AUTOCONF_MACOS_PREREQ(10, 5)    || \
-    BUILD2_AUTOCONF_GLIBC_PREREQ(2, 1)
+#if BUILD2_AUTOCONF_GLIBC_PREREQ(2, 1)
 #  define HAVE_SYS_SENDFILE_H 1
 #endif