diff --git a/UPGRADING.INTERNALS b/UPGRADING.INTERNALS
index 27414f52b3754..ad8125c5d13a1 100644
--- a/UPGRADING.INTERNALS
+++ b/UPGRADING.INTERNALS
@@ -75,11 +75,15 @@ PHP 8.6 INTERNALS UPGRADE NOTES
 2. Build system changes
 ========================
 
+- Abstract:
   . build/gen_stub.php may now generate a _decl.h file in addition to
     the _arginfo.h file, if the stub declares enums and is annotated with
     @generate-c-enums. For each enum the file will contain a C enum. Enum values
     can be compared to the result of zend_enum_fetch_case_id(zend_object*).
 
+- Unix build system changes:
+  . Autoconf minimum required version upgraded to 2.70.
+
 ========================
 3. Module changes
 ========================
diff --git a/Zend/Zend.m4 b/Zend/Zend.m4
index 0e45bdb8af90f..a15d504486fa4 100644
--- a/Zend/Zend.m4
+++ b/Zend/Zend.m4
@@ -133,13 +133,13 @@ dnl
 AC_DEFUN([ZEND_INIT], [dnl
 AC_REQUIRE([AC_PROG_CC])
 
-AC_CHECK_HEADERS(m4_normalize([
+AC_CHECK_HEADERS([
   cpuid.h
   libproc.h
-]))
+])
 
 dnl Check for library functions.
-AC_CHECK_FUNCS(m4_normalize([
+AC_CHECK_FUNCS([
   getpid
   gettid
   kill
@@ -150,7 +150,7 @@ AC_CHECK_FUNCS(m4_normalize([
   pthread_getattr_np
   pthread_stackseg_np
   strnlen
-]))
+])
 
 AC_CHECK_DECL([clock_gettime_nsec_np],
   [AC_DEFINE([HAVE_CLOCK_GETTIME_NSEC_NP], [1],
diff --git a/configure.ac b/configure.ac
index beeed7eb21115..abe864a8ba164 100644
--- a/configure.ac
+++ b/configure.ac
@@ -16,7 +16,7 @@ m4_include([Zend/Zend.m4])
 dnl Basic autoconf initialization, generation of config.nice.
 dnl ----------------------------------------------------------------------------
 
-AC_PREREQ([2.68])
+AC_PREREQ([2.70])
 AC_INIT([PHP],[8.6.0-dev],[https://github.com/php/php-src/issues],[php],[https://www.php.net])
 AC_CONFIG_SRCDIR([main/php_version.h])
 AC_CONFIG_AUX_DIR([build])
@@ -113,11 +113,14 @@ dnl ----------------------------------------------------------------------------
 
 PKG_PROG_PKG_CONFIG
 AC_PROG_CC([cc gcc])
+
+dnl Check if C compiler accepts C11.
+AS_CASE([$ac_prog_cc_stdc], [c99|c89|no],
+  [AC_MSG_ERROR([C compiler would not accept C11 code.])])
+
 PHP_DETECT_ICC
 PHP_DETECT_SUNCC
 
-dnl AC_PROG_CC_C99 is obsolete with autoconf >= 2.70 yet necessary for <= 2.69.
-m4_version_prereq([2.70],,[AC_PROG_CC_C99])
 AC_PROG_CPP
 AC_USE_SYSTEM_EXTENSIONS
 AC_PROG_LN_S
@@ -128,17 +131,6 @@ AS_VAR_IF([cross_compiling], [yes],
     AC_MSG_RESULT([$BUILD_CC])],
   [BUILD_CC=$CC])
 
-dnl The macro AC_PROG_CC_C99 sets the shell variable ac_cv_prog_cc_c99 to 'no'
-dnl if the compiler does not support C99.i.e. does not support any of _Bool,
-dnl flexible arrays, inline, long long int, mixed code and declarations,
-dnl named initialization of structs, restrict, varargs macros, variable
-dnl declarations in for loops and variable length arrays.
-dnl
-dnl https://www.gnu.org/software/autoconf/manual/autoconf-2.60/html_node/C-Compiler.html
-if test "$ac_cv_prog_cc_c99" = no; then
-  AC_MSG_ERROR([C compiler would not accept C99 code])
-fi
-
 dnl Support systems with system libraries in e.g. /usr/lib64.
 PHP_ARG_WITH([libdir],
   [for system library directory],
@@ -370,7 +362,7 @@ dnl Then headers.
 dnl ----------------------------------------------------------------------------
 
 dnl QNX requires unix.h to allow functions in libunix to work properly.
-AC_CHECK_HEADERS(m4_normalize([
+AC_CHECK_HEADERS([
   dirent.h
   sys/param.h
   sys/types.h
@@ -418,7 +410,7 @@ AC_CHECK_HEADERS(m4_normalize([
   nmmintrin.h
   wmmintrin.h
   immintrin.h
-]),,, [dnl
+],,, [dnl
 #ifdef HAVE_SYS_PARAM_H
 #include <sys/param.h>
 #endif
@@ -441,8 +433,6 @@ PHP_BROKEN_GETCWD
 AS_VAR_IF([GCC], [yes], [PHP_BROKEN_GCC_STRLEN_OPT])
 
 dnl Detect the headers required to use makedev, major, and minor.
-dnl Autoconf <= 2.69 didn't check glibc 2.25 deprecated macros in sys/types.h.
-m4_version_prereq([2.70],,[ac_cv_header_sys_types_h_makedev=no])
 AC_HEADER_MAJOR
 
 dnl Checks for typedefs, structures, and compiler characteristics.
@@ -535,7 +525,7 @@ PHP_CHECK_VARIABLE_ATTRIBUTE([aligned])
 dnl Checks for library functions.
 dnl ----------------------------------------------------------------------------
 
-AC_CHECK_FUNCS(m4_normalize([
+AC_CHECK_FUNCS([
   alphasort
   asctime_r
   asprintf
@@ -596,7 +586,7 @@ AC_CHECK_FUNCS(m4_normalize([
   usleep
   utime
   vasprintf
-]))
+])
 
 PHP_ARG_ENABLE([system-glob],
   [whether to use the system glob function],
diff --git a/ext/ldap/config.m4 b/ext/ldap/config.m4
index 14174bd5dc26e..b8edd4008921b 100644
--- a/ext/ldap/config.m4
+++ b/ext/ldap/config.m4
@@ -132,7 +132,7 @@ if test "$PHP_LDAP" != "no"; then
 
   dnl Solaris 2.8 claims to be 2004 API, but doesn't have ldap_parse_reference()
   dnl nor ldap_start_tls_s()
-  AC_CHECK_FUNCS(m4_normalize([
+  AC_CHECK_FUNCS([
     ldap_control_find
     ldap_extended_operation
     ldap_extended_operation_s
@@ -143,7 +143,7 @@ if test "$PHP_LDAP" != "no"; then
     ldap_refresh_s
     ldap_start_tls_s
     ldap_whoami_s
-  ]))
+  ])
 
   dnl Sanity check
   AC_CHECK_FUNC([ldap_sasl_bind_s],,
diff --git a/ext/pcntl/config.m4 b/ext/pcntl/config.m4
index cfe6e80ca1103..0edf92256ca7e 100644
--- a/ext/pcntl/config.m4
+++ b/ext/pcntl/config.m4
@@ -9,7 +9,7 @@ if test "$PHP_PCNTL" != "no"; then
       [AC_MSG_FAILURE([ext/pcntl: required function $function() not found.])])
   done
 
-  AC_CHECK_FUNCS(m4_normalize([
+  AC_CHECK_FUNCS([
     forkx
     getcpuid
     getpriority
@@ -26,7 +26,7 @@ if test "$PHP_PCNTL" != "no"; then
     waitid
     wait6
     syscall
-  ]))
+  ])
 
   AC_CHECK_FUNCS([WIFCONTINUED],,
     [AC_CHECK_DECL([WIFCONTINUED], [AC_DEFINE([HAVE_WIFCONTINUED], [1])],,
diff --git a/ext/posix/config.m4 b/ext/posix/config.m4
index 8655463569536..b0f6b1879593f 100644
--- a/ext/posix/config.m4
+++ b/ext/posix/config.m4
@@ -12,7 +12,7 @@ if test "$PHP_POSIX" = "yes"; then
     [$ext_shared],,
     [-DZEND_ENABLE_STATIC_TSRMLS_CACHE=1])
 
-  AC_CHECK_FUNCS(m4_normalize([
+  AC_CHECK_FUNCS([
     ctermid
     eaccess
     getgrgid_r
@@ -28,7 +28,7 @@ if test "$PHP_POSIX" = "yes"; then
     seteuid
     setrlimit
     setsid
-  ]))
+  ])
 
   dnl Check for makedev. If it's defined as a macro, AC_CHECK_FUNCS won't work.
   dnl Required headers are included by the AC_HEADER_MAJOR logic.
diff --git a/scripts/phpize.m4 b/scripts/phpize.m4
index be7065b786d96..f73871f6a13fd 100644
--- a/scripts/phpize.m4
+++ b/scripts/phpize.m4
@@ -9,7 +9,7 @@ m4_include([build/php_cxx_compile_stdcxx.m4])
 m4_include([build/php.m4])
 m4_include([build/pkg.m4])
 
-AC_PREREQ([2.68])
+AC_PREREQ([2.70])
 AC_INIT
 AC_CONFIG_SRCDIR([config.m4])
 AC_CONFIG_AUX_DIR([build])