diff --git a/m4/ax_append_flag.m4 b/m4/ax_append_flag.m4
index 08f2e07..e8c5312 100644
--- a/m4/ax_append_flag.m4
+++ b/m4/ax_append_flag.m4
@@ -1,5 +1,5 @@
 # ===========================================================================
-#      http://www.gnu.org/software/autoconf-archive/ax_append_flag.html
+#      https://www.gnu.org/software/autoconf-archive/ax_append_flag.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -34,7 +34,7 @@
 #   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
@@ -49,7 +49,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 6
+#serial 7
 
 AC_DEFUN([AX_APPEND_FLAG],
 [dnl
diff --git a/m4/ax_c___attribute__.m4 b/m4/ax_c___attribute__.m4
index cf3d62b..6a1ede1 100644
--- a/m4/ax_c___attribute__.m4
+++ b/m4/ax_c___attribute__.m4
@@ -1,5 +1,5 @@
 # ===========================================================================
-#    http://www.gnu.org/software/autoconf-archive/ax_c___attribute__.html
+#    https://www.gnu.org/software/autoconf-archive/ax_c___attribute__.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -28,7 +28,7 @@
 #   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
@@ -43,7 +43,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 8
+#serial 9
 
 AC_DEFUN([AX_C___ATTRIBUTE__], [
   AC_CACHE_CHECK([for __attribute__], [ax_cv___attribute__],
diff --git a/m4/ax_cflags_warn_all.m4 b/m4/ax_cflags_warn_all.m4
index 1f07799..094577e 100644
--- a/m4/ax_cflags_warn_all.m4
+++ b/m4/ax_cflags_warn_all.m4
@@ -1,5 +1,5 @@
 # ===========================================================================
-#    http://www.gnu.org/software/autoconf-archive/ax_cflags_warn_all.html
+#    https://www.gnu.org/software/autoconf-archive/ax_cflags_warn_all.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -43,7 +43,7 @@
 #   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
@@ -58,7 +58,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 15
+#serial 16
 
 AC_DEFUN([AX_FLAGS_WARN_ALL],[dnl
 AS_VAR_PUSHDEF([FLAGS],[_AC_LANG_PREFIX[]FLAGS])dnl
diff --git a/m4/ax_require_defined.m4 b/m4/ax_require_defined.m4
index cae1111..17c3eab 100644
--- a/m4/ax_require_defined.m4
+++ b/m4/ax_require_defined.m4
@@ -1,5 +1,5 @@
 # ===========================================================================
-#    http://www.gnu.org/software/autoconf-archive/ax_require_defined.html
+#    https://www.gnu.org/software/autoconf-archive/ax_require_defined.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -30,7 +30,7 @@
 #   and this notice are preserved. This file is offered as-is, without any
 #   warranty.
 
-#serial 1
+#serial 2
 
 AC_DEFUN([AX_REQUIRE_DEFINED], [dnl
   m4_ifndef([$1], [m4_fatal([macro ]$1[ is not defined; is a m4 file missing?])])