diff --git a/include/fast_float/float_common.h b/include/fast_float/float_common.h
index ee7a6d0..479febc 100644
--- a/include/fast_float/float_common.h
+++ b/include/fast_float/float_common.h
@@ -203,15 +203,27 @@ using parse_options = parse_options_t<char>;
 // the hot frame and hurt ILP on some targets). Used at the call site as
 //   if fastfloat_unlikely(cond) { ... }
 // (the macro supplies the parentheses). It expands to the standard [[unlikely]]
-// attribute in C++20 or newer, otherwise to __builtin_expect on GCC/Clang, or
+// attribute when supported, otherwise to __builtin_expect on GCC/Clang, or
 // to a no-op elsewhere (e.g. pre-C++20 MSVC, which has no equivalent hint).
-// The [[unlikely]] branch is gated on the language version, not just on
-// __has_cpp_attribute: GCC and Clang report the attribute as available even
-// under -std=c++17, where using it would trip -Wc++20-extensions/-Werror.
-#if (__cplusplus >= 202002L ||                                                 \
-     (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)) &&                        \
-    defined(__has_cpp_attribute) && __has_cpp_attribute(unlikely) >= 201803L
+#ifdef __has_cpp_attribute
+#if __has_cpp_attribute(unlikely) >= 201803L
+#define FASTFLOAT_USE_UNLIKELY_ATTR 1
+#endif
+#endif
+
+#ifdef FASTFLOAT_USE_UNLIKELY_ATTR
+// We have to disable -Wc++20-extensions for the [[unlikely]] attribute
+// See comment for @jwakely at
+// https://github.com/fastfloat/fast_float/pull/387#discussion_r3366943539
+// This is unfortunate.
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++20-extensions"
+#endif
 #define fastfloat_unlikely(x) (x) [[unlikely]]
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
 #elif defined(__GNUC__) || defined(__clang__)
 #define fastfloat_unlikely(x) (__builtin_expect(!!(x), 0))
 #else
diff --git a/include/fast_float/parse_number.h b/include/fast_float/parse_number.h
index a844bc8..1071573 100644
--- a/include/fast_float/parse_number.h
+++ b/include/fast_float/parse_number.h
@@ -351,6 +351,10 @@ from_chars_float_advanced(UC const *first, UC const *last, T &value,
   // Slow path A (rare): > 19 significant digits. The no-span parse left the
   // mantissa un-truncated and skipped the span-based recompute; the cold helper
   // re-parses with spans and runs the full algorithm.
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++20-extensions"
+#endif
   if fastfloat_unlikely (pns.too_many_digits) {
     return parse_number_slow_path<T, UC>(first, last, value, options, bjf);
   }
@@ -371,6 +375,9 @@ from_chars_float_advanced(UC const *first, UC const *last, T &value,
   if fastfloat_unlikely (am.power2 < 0) {
     return parse_number_slow_path<T, UC>(first, last, value, options, bjf);
   }
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
   to_float(pns.negative, am, value);
   // Test for over/underflow.
   if ((pns.mantissa != 0 && am.mantissa == 0 && am.power2 == 0) ||