diff --git a/tests/ui/c-variadic/variadic-ffi-no-fixed-args.rs b/tests/ui/c-variadic/variadic-ffi-no-fixed-args.rs
index 588c15a1829..b8841e88c4f 100644
--- a/tests/ui/c-variadic/variadic-ffi-no-fixed-args.rs
+++ b/tests/ui/c-variadic/variadic-ffi-no-fixed-args.rs
@@ -1,6 +1,9 @@
+//@ build-pass
+
+// Supported since C23
+// https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2975.pdf
 extern "C" {
     fn foo(...);
-//~^ ERROR C-variadic function must be declared with at least one named argument
 }
 
 fn main() {}
diff --git a/tests/ui/c-variadic/variadic-ffi-no-fixed-args.stderr b/tests/ui/c-variadic/variadic-ffi-no-fixed-args.stderr
deleted file mode 100644
index e268ef3fa68..00000000000
--- a/tests/ui/c-variadic/variadic-ffi-no-fixed-args.stderr
+++ /dev/null
@@ -1,8 +0,0 @@
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-no-fixed-args.rs:2:12
-   |
-LL |     fn foo(...);
-   |            ^^^
-
-error: aborting due to 1 previous error
-
diff --git a/tests/ui/parser/variadic-ffi-semantic-restrictions.rs b/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
index a2d2388ff50..11126dbc65d 100644
--- a/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
+++ b/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
@@ -8,14 +8,12 @@ fn f1_1(x: isize, ...) {}
 
 fn f1_2(...) {}
 //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
-//~| ERROR C-variadic function must be declared with at least one named argument
 
 extern "C" fn f2_1(x: isize, ...) {}
 //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 
 extern "C" fn f2_2(...) {}
 //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
-//~| ERROR C-variadic function must be declared with at least one named argument
 
 extern "C" fn f2_3(..., x: isize) {}
 //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
@@ -26,7 +24,6 @@ extern "C" fn f3_1(x: isize, ...) {}
 
 extern "C" fn f3_2(...) {}
 //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
-//~| ERROR C-variadic function must be declared with at least one named argument
 
 extern "C" fn f3_3(..., x: isize) {}
 //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
@@ -47,8 +44,6 @@ extern "C" fn f3_3(..., x: isize) {}
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 extern "C" {
-    fn e_f1(...);
-    //~^ ERROR C-variadic function must be declared with at least one named argument
     fn e_f2(..., x: isize);
     //~^ ERROR `...` must be the last argument of a C-variadic function
 }
@@ -60,7 +55,6 @@ fn i_f1(x: isize, ...) {}
     //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     fn i_f2(...) {}
     //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
-    //~| ERROR C-variadic function must be declared with at least one named argument
     fn i_f3(..., x: isize, ...) {}
     //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| ERROR `...` must be the last argument of a C-variadic function
@@ -80,10 +74,8 @@ fn t_f1(x: isize, ...) {}
     //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     fn t_f3(...) {}
     //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
-    //~| ERROR C-variadic function must be declared with at least one named argument
     fn t_f4(...);
     //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
-    //~| ERROR C-variadic function must be declared with at least one named argument
     fn t_f5(..., x: isize) {}
     //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| ERROR `...` must be the last argument of a C-variadic function
diff --git a/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr b/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
index 6a65ed79d4f..f71e3863440 100644
--- a/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
+++ b/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
@@ -4,12 +4,6 @@ error: only foreign or `unsafe extern "C"` functions may be C-variadic
 LL | fn f1_1(x: isize, ...) {}
    |                   ^^^
 
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:9:9
-   |
-LL | fn f1_2(...) {}
-   |         ^^^
-
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
   --> $DIR/variadic-ffi-semantic-restrictions.rs:9:9
    |
@@ -17,91 +11,79 @@ LL | fn f1_2(...) {}
    |         ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:13:30
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:12:30
    |
 LL | extern "C" fn f2_1(x: isize, ...) {}
    |                              ^^^
 
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:16:20
-   |
-LL | extern "C" fn f2_2(...) {}
-   |                    ^^^
-
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:16:20
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:15:20
    |
 LL | extern "C" fn f2_2(...) {}
    |                    ^^^
 
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:20:20
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:18:20
    |
 LL | extern "C" fn f2_3(..., x: isize) {}
    |                    ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:20:20
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:18:20
    |
 LL | extern "C" fn f2_3(..., x: isize) {}
    |                    ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:24:30
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:22:30
    |
 LL | extern "C" fn f3_1(x: isize, ...) {}
    |                              ^^^
 
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:27:20
-   |
-LL | extern "C" fn f3_2(...) {}
-   |                    ^^^
-
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:27:20
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:25:20
    |
 LL | extern "C" fn f3_2(...) {}
    |                    ^^^
 
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:31:20
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:28:20
    |
 LL | extern "C" fn f3_3(..., x: isize) {}
    |                    ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:31:20
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:28:20
    |
 LL | extern "C" fn f3_3(..., x: isize) {}
    |                    ^^^
 
 error: functions cannot be both `const` and C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:35:1
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:32:1
    |
 LL | const unsafe extern "C" fn f4_1(x: isize, ...) {}
    | ^^^^^ `const` because of this             ^^^ C-variadic because of this
 
 error: functions cannot be both `const` and C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:39:1
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:36:1
    |
 LL | const extern "C" fn f4_2(x: isize, ...) {}
    | ^^^^^ `const` because of this      ^^^ C-variadic because of this
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:39:36
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:36:36
    |
 LL | const extern "C" fn f4_2(x: isize, ...) {}
    |                                    ^^^
 
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:44:26
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:41:26
    |
 LL | const extern "C" fn f4_3(..., x: isize, ...) {}
    |                          ^^^
 
 error: functions cannot be both `const` and C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:44:1
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:41:1
    |
 LL | const extern "C" fn f4_3(..., x: isize, ...) {}
    | ^^^^^                    ^^^            ^^^ C-variadic because of this
@@ -110,67 +92,55 @@ LL | const extern "C" fn f4_3(..., x: isize, ...) {}
    | `const` because of this
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:44:26
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:41:26
    |
 LL | const extern "C" fn f4_3(..., x: isize, ...) {}
    |                          ^^^            ^^^
 
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:50:13
-   |
-LL |     fn e_f1(...);
-   |             ^^^
-
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:52:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:47:13
    |
 LL |     fn e_f2(..., x: isize);
    |             ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:59:23
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:54:23
    |
 LL |     fn i_f1(x: isize, ...) {}
    |                       ^^^
 
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:61:13
-   |
-LL |     fn i_f2(...) {}
-   |             ^^^
-
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:61:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:56:13
    |
 LL |     fn i_f2(...) {}
    |             ^^^
 
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:64:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:58:13
    |
 LL |     fn i_f3(..., x: isize, ...) {}
    |             ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:64:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:58:13
    |
 LL |     fn i_f3(..., x: isize, ...) {}
    |             ^^^            ^^^
 
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:67:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:61:13
    |
 LL |     fn i_f4(..., x: isize, ...) {}
    |             ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:67:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:61:13
    |
 LL |     fn i_f4(..., x: isize, ...) {}
    |             ^^^            ^^^
 
 error: functions cannot be both `const` and C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:70:5
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:64:5
    |
 LL |     const fn i_f5(x: isize, ...) {}
    |     ^^^^^                   ^^^ C-variadic because of this
@@ -178,73 +148,61 @@ LL |     const fn i_f5(x: isize, ...) {}
    |     `const` because of this
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:70:29
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:64:29
    |
 LL |     const fn i_f5(x: isize, ...) {}
    |                             ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:77:23
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:71:23
    |
 LL |     fn t_f1(x: isize, ...) {}
    |                       ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:79:23
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:73:23
    |
 LL |     fn t_f2(x: isize, ...);
    |                       ^^^
 
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:81:13
+error: only foreign or `unsafe extern "C"` functions may be C-variadic
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:75:13
    |
 LL |     fn t_f3(...) {}
    |             ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:81:13
-   |
-LL |     fn t_f3(...) {}
-   |             ^^^
-
-error: C-variadic function must be declared with at least one named argument
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:84:13
-   |
-LL |     fn t_f4(...);
-   |             ^^^
-
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:84:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:77:13
    |
 LL |     fn t_f4(...);
    |             ^^^
 
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:87:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:79:13
    |
 LL |     fn t_f5(..., x: isize) {}
    |             ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:87:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:79:13
    |
 LL |     fn t_f5(..., x: isize) {}
    |             ^^^
 
 error: `...` must be the last argument of a C-variadic function
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:90:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:82:13
    |
 LL |     fn t_f6(..., x: isize);
    |             ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:90:13
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:82:13
    |
 LL |     fn t_f6(..., x: isize);
    |             ^^^
 
 error[E0493]: destructor of `VaListImpl<'_>` cannot be evaluated at compile-time
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:35:43
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:32:43
    |
 LL | const unsafe extern "C" fn f4_1(x: isize, ...) {}
    |                                           ^^^   - value is dropped here
@@ -252,7 +210,7 @@ LL | const unsafe extern "C" fn f4_1(x: isize, ...) {}
    |                                           the destructor for this type cannot be evaluated in constant functions
 
 error[E0493]: destructor of `VaListImpl<'_>` cannot be evaluated at compile-time
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:39:36
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:36:36
    |
 LL | const extern "C" fn f4_2(x: isize, ...) {}
    |                                    ^^^   - value is dropped here
@@ -260,13 +218,13 @@ LL | const extern "C" fn f4_2(x: isize, ...) {}
    |                                    the destructor for this type cannot be evaluated in constant functions
 
 error[E0493]: destructor of `VaListImpl<'_>` cannot be evaluated at compile-time
-  --> $DIR/variadic-ffi-semantic-restrictions.rs:70:29
+  --> $DIR/variadic-ffi-semantic-restrictions.rs:64:29
    |
 LL |     const fn i_f5(x: isize, ...) {}
    |                             ^^^   - value is dropped here
    |                             |
    |                             the destructor for this type cannot be evaluated in constant functions
 
-error: aborting due to 43 previous errors
+error: aborting due to 36 previous errors
 
 For more information about this error, try `rustc --explain E0493`.