diff --git a/stl/inc/format b/stl/inc/format
index e09d61e5f3..0ffd0c8ddb 100644
--- a/stl/inc/format
+++ b/stl/inc/format
@@ -3519,7 +3519,10 @@ struct _Format_checker {
     consteval explicit _Format_checker(basic_string_view<_CharT> _Fmt) noexcept
         : _Parse_context(_Fmt, _Num_args), _Parse_funcs{&_Compile_time_parse_format_specs<_Args, _ParseContext>...} {}
     constexpr void _On_text(const _CharT*, const _CharT*) const noexcept {}
-    constexpr void _On_replacement_field(size_t, const _CharT*) const noexcept {}
+    constexpr void _On_replacement_field(const size_t _Id, const _CharT*) const {
+        _ParseContext _Parse_ctx({});
+        (void) _Parse_funcs[_Id](_Parse_ctx);
+    }
     constexpr const _CharT* _On_format_specs(const size_t _Id, const _CharT* _First, const _CharT*) {
         _Parse_context.advance_to(_Parse_context.begin() + (_First - _Parse_context.begin()._Unwrapped()));
         if (_Id < _Num_args) {
diff --git a/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp b/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
index e15a100d78..928ff8aa89 100644
--- a/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
@@ -57,7 +57,7 @@ struct not_const_formattable_type {
 
 template <>
 struct std::formatter<basic_custom_formattable_type, char> {
-    basic_format_parse_context<char>::iterator parse(basic_format_parse_context<char>& parse_ctx) {
+    constexpr basic_format_parse_context<char>::iterator parse(basic_format_parse_context<char>& parse_ctx) {
         if (parse_ctx.begin() != parse_ctx.end()) {
             throw format_error{"only empty specs please"};
         }
@@ -71,7 +71,7 @@ struct std::formatter<basic_custom_formattable_type, char> {
 
 template <>
 struct std::formatter<not_const_formattable_type, char> {
-    basic_format_parse_context<char>::iterator parse(basic_format_parse_context<char>& parse_ctx) {
+    constexpr basic_format_parse_context<char>::iterator parse(basic_format_parse_context<char>& parse_ctx) {
         if (parse_ctx.begin() != parse_ctx.end()) {
             throw format_error{"only empty specs please"};
         }