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 6bc20e4..0e898ed 100644
--- a/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_NETINET_IN6_H.h
+++ b/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_NETINET_IN6_H.h
@@ -6,11 +6,11 @@
 
 #undef HAVE_NETINET_IN6_H
 
-/* No decent info...
+/* 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(__linux__)   || \
-    defined(__FreeBSD__) || \
-    defined(__OpenBSD__) || \
+#if defined(__OpenBSD__) || \
     defined(__NetBSD__)  || \
     defined(BUILD2_AUTOCONF_MACOS)
 #  define HAVE_NETINET_IN6_H 1
diff --git a/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_STRUCT_SOCKADDR_IN6.h b/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_STRUCT_SOCKADDR_IN6.h
index 8cb1510..fe01778 100644
--- a/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_STRUCT_SOCKADDR_IN6.h
+++ b/libbuild2-autoconf/libbuild2/autoconf/checks/HAVE_STRUCT_SOCKADDR_IN6.h
@@ -6,9 +6,11 @@
 
 #undef HAVE_STRUCT_SOCKADDR_IN6
 
-/* Since OpenBSD ~4.2, FreeBSD ~7.0, NetBSD 2.1, Mac OS X 10.6, Windows
+/* Since glibc 2.1, OpenBSD ~4.2, FreeBSD ~7.0, NetBSD 2.1, Mac OS X 10.6,
+ * Windows
  */
-#if BUILD2_AUTOCONF_OPENBSD_PREREQ(200705)  || \
+#if BUILD2_AUTOCONF_GLIBC_PREREQ(2, 1)      || \
+    BUILD2_AUTOCONF_OPENBSD_PREREQ(200705)  || \
     BUILD2_AUTOCONF_FREEBSD_PREREQ(7, 0)    || \
     BUILD2_AUTOCONF_NETBSD_PREREQ(2, 1)     || \
     BUILD2_AUTOCONF_MACOS_PREREQ(10, 6)     || \