diff --git a/m4.include/ax_gcc_func_attribute.m4 b/m4.include/ax_gcc_func_attribute.m4
index 098c9aadf..fa4e089d6 100644
--- a/m4.include/ax_gcc_func_attribute.m4
+++ b/m4.include/ax_gcc_func_attribute.m4
@@ -42,6 +42,7 @@
 #    flatten
 #    format
 #    format_arg
+#    gnu_format
 #    gnu_inline
 #    hot
 #    ifunc
@@ -77,7 +78,7 @@
 #   and this notice are preserved.  This file is offered as-is, without any
 #   warranty.
 
-#serial 9
+#serial 13
 
 AC_DEFUN([AX_GCC_FUNC_ATTRIBUTE], [
     AS_VAR_PUSHDEF([ac_var], [ax_cv_have_func_attribute_$1])
@@ -132,7 +133,7 @@ AC_DEFUN([AX_GCC_FUNC_ATTRIBUTE], [
                     int foo( void ) __attribute__(($1));
                 ],
                 [fallthrough], [
-                    int foo( void ) {switch (0) { case 1: __attribute__(($1)); case 2: break ; }};
+                    void foo( int x ) {switch (x) { case 1: __attribute__(($1)); case 2: break ; }};
                 ],
                 [flatten], [
                     int foo( void ) __attribute__(($1));
@@ -140,6 +141,9 @@ AC_DEFUN([AX_GCC_FUNC_ATTRIBUTE], [
                 [format], [
                     int foo(const char *p, ...) __attribute__(($1(printf, 1, 2)));
                 ],
+                [gnu_format], [
+                    int foo(const char *p, ...) __attribute__((format(gnu_printf, 1, 2)));
+                ],
                 [format_arg], [
                     char *foo(const char *p) __attribute__(($1(1)));
                 ],
@@ -224,7 +228,7 @@ AC_DEFUN([AX_GCC_FUNC_ATTRIBUTE], [
             dnl GCC doesn't exit with an error if an unknown attribute is
             dnl provided but only outputs a warning, so accept the attribute
             dnl only if no warning were issued.
-            [AS_IF([test -s conftest.err],
+            [AS_IF([grep -- -Wattributes conftest.err],
                 [AS_VAR_SET([ac_var], [no])],
                 [AS_VAR_SET([ac_var], [yes])])],
             [AS_VAR_SET([ac_var], [no])])