diff --git a/license.txt b/license.txt
index 3f412a4415798d63b7689889a7fdaab8f99dc050..28385cc86e70690e2f60efe23fec97ab1ce7326e 100644
--- a/license.txt
+++ b/license.txt
@@ -311,7 +311,7 @@ License: LGPL-2.1+
 
 Files: m4/ax_matlab_arch.m4 m4/ax_matlab.m4 m4/ax_mexext.m4
 Copyright: 2002-2003 Ralph Schleicher
-           2009-2019 Dynare Team
+           2009-2021 Dynare Team
 License: GPL-2+ with Autoconf exception
 
 Files: scripts/dynare.el
diff --git a/m4/ax_gsl.m4 b/m4/ax_gsl.m4
index 1bbd2be9d3c1043194dee52bb49abfddc8f423e0..a14cf515a3d4e5023f453bf0c82f1fa860aac402 100644
--- a/m4/ax_gsl.m4
+++ b/m4/ax_gsl.m4
@@ -2,7 +2,7 @@ dnl Detect GSL.
 dnl We don't use the official M4 macro since it relies on the script gsl-config,
 dnl which does not work when cross-compiling.
 dnl
-dnl Copyright © 2010-2012 Dynare Team
+dnl Copyright © 2010-2021 Dynare Team
 dnl
 dnl This file is part of Dynare.
 dnl
@@ -21,7 +21,7 @@ dnl along with Dynare.  If not, see <https://www.gnu.org/licenses/>.
 
 AC_DEFUN([AX_GSL],
 [
-AC_ARG_WITH(gsl, AC_HELP_STRING([--with-gsl=DIR], [prefix to GSL installation]),
+AC_ARG_WITH(gsl, AS_HELP_STRING([--with-gsl=DIR], [prefix to GSL installation]),
             gsl_prefix="$withval", gsl_prefix="")
 
   has_gsl=yes
diff --git a/m4/ax_matio.m4 b/m4/ax_matio.m4
index 00cef25aa64569a0ea81787b7e18d30f56d81149..caab9ef4c70ab3d1141d075a3b116f89555b9cf7 100644
--- a/m4/ax_matio.m4
+++ b/m4/ax_matio.m4
@@ -1,6 +1,6 @@
 dnl Detect the MATIO Library.
 dnl
-dnl Copyright © 2012-2014 Dynare Team
+dnl Copyright © 2012-2021 Dynare Team
 dnl
 dnl This file is part of Dynare.
 dnl
@@ -19,7 +19,7 @@ dnl along with Dynare.  If not, see <https://www.gnu.org/licenses/>.
 
 AC_DEFUN([AX_MATIO],
 [
-AC_ARG_WITH(matio, AC_HELP_STRING([--with-matio=DIR], [prefix to MATIO installation]),
+AC_ARG_WITH(matio, AS_HELP_STRING([--with-matio=DIR], [prefix to MATIO installation]),
             matio_prefix="$withval", matio_prefix="")
 
   has_matio=yes
diff --git a/m4/ax_matlab.m4 b/m4/ax_matlab.m4
index 16330420b31aa347569282ff32aa147d030efa22..58e6e753a12d4286e1c4bddaea481df4e5c31abd 100644
--- a/m4/ax_matlab.m4
+++ b/m4/ax_matlab.m4
@@ -1,7 +1,7 @@
 dnl ax_matlab.m4 --- check for MATLAB.
 dnl
 dnl Copyright © 2000-2003 Ralph Schleicher
-dnl Copyright © 2009 Dynare Team
+dnl Copyright © 2009-2021 Dynare Team
 dnl
 dnl This program is free software; you can redistribute it and/or
 dnl modify it under the terms of the GNU General Public License as
@@ -31,7 +31,7 @@ AC_DEFUN([AX_MATLAB],
 [dnl
 AC_PREREQ([2.50])
 ax_enable_matlab=
-AC_ARG_WITH([matlab], AC_HELP_STRING([--with-matlab=ARG], [check for MATLAB [[yes]]]),
+AC_ARG_WITH([matlab], AS_HELP_STRING([--with-matlab=ARG], [check for MATLAB [[yes]]]),
 [case $withval in
   yes | no)
     # Explicitly enable or disable MATLAB but determine
diff --git a/m4/ax_octave.m4 b/m4/ax_octave.m4
index 3708c999b1c680d142d323675735f00bf8e9442d..6bd400d6e06bc022632edff2e1ed4193b48ead91 100644
--- a/m4/ax_octave.m4
+++ b/m4/ax_octave.m4
@@ -1,6 +1,6 @@
 dnl ax_octave.m4 --- check for Octave
 dnl
-dnl Copyright © 2020 Dynare Team
+dnl Copyright © 2020-2021 Dynare Team
 dnl
 dnl This program is free software; you can redistribute it and/or
 dnl modify it under the terms of the GNU General Public License as
@@ -30,7 +30,7 @@ dnl of that program.
 # Sets ax_enable_octave=yes if successful, ax_enable_octave=no otherwise
 AC_DEFUN([AX_OCTAVE],
 [dnl
-AC_ARG_WITH([octave], AC_HELP_STRING([--with-octave=PATH], [Path to search for Octave installation]),
+AC_ARG_WITH([octave], AS_HELP_STRING([--with-octave=PATH], [Path to search for Octave installation]),
 [
   if test -n "$withval"; then
     if test -x "$withval/bin/octave" && test -x "$withval/bin/mkoctfile"; then
diff --git a/m4/ax_slicot.m4 b/m4/ax_slicot.m4
index ae9793693d94d25753c75c8979ef51a703288d6e..e329d0b172f1c5c05387d4cc167268d5243d7f94 100644
--- a/m4/ax_slicot.m4
+++ b/m4/ax_slicot.m4
@@ -28,7 +28,7 @@ AC_DEFUN([AX_SLICOT],
     AC_MSG_ERROR([Argument to autoconf slicot macro must be either 'matlab' or 'octave'])
   fi
 
-  AC_ARG_WITH(slicot, AC_HELP_STRING([--with-slicot=DIR], [prefix to SLICOT installation]),
+  AC_ARG_WITH(slicot, AS_HELP_STRING([--with-slicot=DIR], [prefix to SLICOT installation]),
               slicot_prefix="$withval", slicot_prefix="")
   has_slicot=yes
 
diff --git a/mex/build/matlab/configure.ac b/mex/build/matlab/configure.ac
index 3476c4e6e76ce3ffe088f11239a7e0f12dff32cc..06182ea8bab8e3aade8f87472d9b6aea45f4776d 100644
--- a/mex/build/matlab/configure.ac
+++ b/mex/build/matlab/configure.ac
@@ -47,7 +47,6 @@ esac
 
 AC_PROG_FC
 AC_PROG_CC
-AC_PROG_CC_C99
 AC_PROG_CXX
 AX_CXX_COMPILE_STDCXX_17
 AC_PROG_RANLIB
diff --git a/mex/build/octave/configure.ac b/mex/build/octave/configure.ac
index 38ea69da42170679357ab78d8cecdf2d8525616d..9781b3c97afbade65fe2279bdebc527617a9df6d 100644
--- a/mex/build/octave/configure.ac
+++ b/mex/build/octave/configure.ac
@@ -43,7 +43,6 @@ AX_COMPARE_VERSION([$OCTAVE_VERSION], [lt], [6.2.0], [AC_MSG_ERROR([Your Octave
 
 AC_PROG_FC
 AC_PROG_CC
-AC_PROG_CC_C99
 AC_PROG_CXX
 AX_CXX_COMPILE_STDCXX_17
 AC_PROG_RANLIB