diff --git a/configure b/configure
index 613a9b839bd..a0b04c03951 100755
--- a/configure
+++ b/configure
@@ -3949,6 +3949,130 @@ else
   fi
 fi
 
+# We use C constructs that became invalid in C23.  Check if the compiler
+# reports a standard higher than C17, with the flags selected above (so the
+# user can control the language level explicitly to avoid the gcc/clang-only
+# fallback logic below if preferred).
+{ $as_echo "$as_me:$LINENO: checking whether $CC reports a C standard higher than ISO C17" >&5
+$as_echo_n "checking whether $CC reports a C standard higher than ISO C17... " >&6; }
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+int
+main ()
+{
+#if __STDC_VERSION__ > 201710L
+choke me
+#endif
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  POSTC17=no
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	POSTC17=yes
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+{ $as_echo "$as_me:$LINENO: result: ${POSTC17}" >&5
+$as_echo "${POSTC17}" >&6; }
+
+# If a too recent standard was detected with the user's CFLAGS, try asking for
+# C17 with GNU extensions explicitly.
+if test "$POSTC17" = yes; then
+  old_CFLAGS="$CFLAGS"
+  { $as_echo "$as_me:$LINENO: checking whether $CC supports -std=gnu17" >&5
+$as_echo_n "checking whether $CC supports -std=gnu17... " >&6; }
+if test "${pgac_cv_prog_cc_cflags__std_gnu17+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -std=gnu17"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  pgac_cv_prog_cc_cflags__std_gnu17=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	pgac_cv_prog_cc_cflags__std_gnu17=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+fi
+{ $as_echo "$as_me:$LINENO: result: $pgac_cv_prog_cc_cflags__std_gnu17" >&5
+$as_echo "$pgac_cv_prog_cc_cflags__std_gnu17" >&6; }
+if test x"$pgac_cv_prog_cc_cflags__std_gnu17" = x"yes"; then
+  CFLAGS="$CFLAGS -std=gnu17"
+fi
+
+  if test "$CFLAGS" = "$old_CFLAGS"; then
+    { { $as_echo "$as_me:$LINENO: error: cannot proceed" >&5
+$as_echo "$as_me: error: cannot proceed" >&2;}
+   { (exit 1); exit 1; }; }
+  fi
+fi
+
 # set CFLAGS_VECTOR from the environment, if available
 if test "$ac_env_CFLAGS_VECTOR_set" = set; then
   CFLAGS_VECTOR=$ac_env_CFLAGS_VECTOR_value
diff --git a/configure.in b/configure.in
index 6a1e17fb048..0daf864ca8d 100644
--- a/configure.in
+++ b/configure.in
@@ -400,6 +400,26 @@ else
   fi
 fi
 
+# We use C constructs that became invalid in C23.  Check if the compiler
+# reports a standard higher than C17, with the flags selected above (so the
+# user can control the language level explicitly to avoid the gcc/clang-only
+# fallback logic below if preferred).
+AC_MSG_CHECKING([whether $CC reports a C standard higher than ISO C17])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [@%:@if __STDC_VERSION__ > 201710L
+choke me
+@%:@endif])], [POSTC17=no], [POSTC17=yes])
+AC_MSG_RESULT(${POSTC17})
+
+# If a too recent standard was detected with the user's CFLAGS, try asking for
+# C17 with GNU extensions explicitly.
+if test "$POSTC17" = yes; then
+  old_CFLAGS="$CFLAGS"
+  PGAC_PROG_CC_CFLAGS_OPT([-std=gnu17])
+  if test "$CFLAGS" = "$old_CFLAGS"; then
+    AC_MSG_ERROR([cannot proceed])
+  fi
+fi
+
 # set CFLAGS_VECTOR from the environment, if available
 if test "$ac_env_CFLAGS_VECTOR_set" = set; then
   CFLAGS_VECTOR=$ac_env_CFLAGS_VECTOR_value