diff --git a/m4/ax_append_link_flags.m4 b/m4/ax_append_link_flags.m4
index fd70fc72..6f7f1745 100644
--- a/m4/ax_append_link_flags.m4
+++ b/m4/ax_append_link_flags.m4
@@ -1,5 +1,5 @@
 # ===========================================================================
-#   http://www.gnu.org/software/autoconf-archive/ax_append_link_flags.html
+#   https://www.gnu.org/software/autoconf-archive/ax_append_link_flags.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -39,7 +39,7 @@
 #   Public License for more details.
 #
 #   You should have received a copy of the GNU General Public License along
-#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
 #
 #   As a special exception, the respective Autoconf Macro's copyright owner
 #   gives unlimited permission to copy, distribute and modify the configure
@@ -54,7 +54,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 5
+#serial 6
 
 AC_DEFUN([AX_APPEND_LINK_FLAGS],
 [AX_REQUIRE_DEFINED([AX_CHECK_LINK_FLAG])