https://bugs.gentoo.org/932579
https://github.com/boostorg/charconv/pull/183
--- a/boost/charconv/detail/bit_layouts.hpp
+++ b/boost/charconv/detail/bit_layouts.hpp
@@ -107,6 +107,7 @@ struct IEEEl2bits
 
 #else // Unsupported long double representation
 #  define BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
+#  define BOOST_CHARCONV_LDBL_BITS -1
 #endif
 
 struct IEEEbinary128
--- a/boost/charconv/from_chars.hpp
+++ b/boost/charconv/from_chars.hpp
@@ -139,7 +139,10 @@ BOOST_CHARCONV_GCC5_CONSTEXPR from_chars_result from_chars(boost::core::string_v
 
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(const char* first, const char* last, float& value, chars_format fmt = chars_format::general) noexcept;
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(const char* first, const char* last, double& value, chars_format fmt = chars_format::general) noexcept;
+
+#ifndef BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(const char* first, const char* last, long double& value, chars_format fmt = chars_format::general) noexcept;
+#endif
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(const char* first, const char* last, __float128& value, chars_format fmt = chars_format::general) noexcept;
@@ -164,7 +167,10 @@ BOOST_CHARCONV_DECL from_chars_result from_chars_erange(const char* first, const
 
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(boost::core::string_view sv, float& value, chars_format fmt = chars_format::general) noexcept;
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(boost::core::string_view sv, double& value, chars_format fmt = chars_format::general) noexcept;
+
+#ifndef BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(boost::core::string_view sv, long double& value, chars_format fmt = chars_format::general) noexcept;
+#endif
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 BOOST_CHARCONV_DECL from_chars_result from_chars_erange(boost::core::string_view sv, __float128& value, chars_format fmt = chars_format::general) noexcept;
@@ -193,7 +199,10 @@ BOOST_CHARCONV_DECL from_chars_result from_chars_erange(boost::core::string_view
 
 BOOST_CHARCONV_DECL from_chars_result from_chars(const char* first, const char* last, float& value, chars_format fmt = chars_format::general) noexcept;
 BOOST_CHARCONV_DECL from_chars_result from_chars(const char* first, const char* last, double& value, chars_format fmt = chars_format::general) noexcept;
+
+#ifndef BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
 BOOST_CHARCONV_DECL from_chars_result from_chars(const char* first, const char* last, long double& value, chars_format fmt = chars_format::general) noexcept;
+#endif
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 BOOST_CHARCONV_DECL from_chars_result from_chars(const char* first, const char* last, __float128& value, chars_format fmt = chars_format::general) noexcept;
@@ -216,7 +225,10 @@ BOOST_CHARCONV_DECL from_chars_result from_chars(const char* first, const char*
 
 BOOST_CHARCONV_DECL from_chars_result from_chars(boost::core::string_view sv, float& value, chars_format fmt = chars_format::general) noexcept;
 BOOST_CHARCONV_DECL from_chars_result from_chars(boost::core::string_view sv, double& value, chars_format fmt = chars_format::general) noexcept;
+
+#ifndef BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
 BOOST_CHARCONV_DECL from_chars_result from_chars(boost::core::string_view sv, long double& value, chars_format fmt = chars_format::general) noexcept;
+#endif
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 BOOST_CHARCONV_DECL from_chars_result from_chars(boost::core::string_view sv, __float128& value, chars_format fmt = chars_format::general) noexcept;
--- a/libs/charconv/src/from_chars.cpp
+++ b/libs/charconv/src/from_chars.cpp
@@ -205,7 +205,7 @@ boost::charconv::from_chars_result boost::charconv::from_chars_erange(const char
     return r;
 }
 
-#else
+#elif !defined(BOOST_MATH_UNSUPPORTED_LONG_DOUBLE)
 
 boost::charconv::from_chars_result boost::charconv::from_chars_erange(const char* first, const char* last, long double& value, boost::charconv::chars_format fmt) noexcept
 {
@@ -299,10 +299,12 @@ boost::charconv::from_chars_result boost::charconv::from_chars_erange(boost::cor
     return boost::charconv::from_chars_erange(sv.data(), sv.data() + sv.size(), value, fmt);
 }
 
+#ifndef BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
 boost::charconv::from_chars_result boost::charconv::from_chars_erange(boost::core::string_view sv, long double& value, boost::charconv::chars_format fmt) noexcept
 {
     return boost::charconv::from_chars_erange(sv.data(), sv.data() + sv.size(), value, fmt);
 }
+#endif
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 boost::charconv::from_chars_result boost::charconv::from_chars_erange(boost::core::string_view sv, __float128& value, boost::charconv::chars_format fmt) noexcept
@@ -372,10 +374,12 @@ boost::charconv::from_chars_result boost::charconv::from_chars(const char* first
     return from_chars_strict_impl(first, last, value, fmt);
 }
 
+#ifndef BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
 boost::charconv::from_chars_result boost::charconv::from_chars(const char* first, const char* last, long double& value, boost::charconv::chars_format fmt) noexcept
 {
     return from_chars_strict_impl(first, last, value, fmt);
 }
+#endif
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 boost::charconv::from_chars_result boost::charconv::from_chars(const char* first, const char* last, __float128& value, boost::charconv::chars_format fmt) noexcept
@@ -429,10 +433,12 @@ boost::charconv::from_chars_result boost::charconv::from_chars(boost::core::stri
     return from_chars_strict_impl(sv.data(), sv.data() + sv.size(), value, fmt);
 }
 
+#ifndef BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
 boost::charconv::from_chars_result boost::charconv::from_chars(boost::core::string_view sv, long double& value, boost::charconv::chars_format fmt) noexcept
 {
     return from_chars_strict_impl(sv.data(), sv.data() + sv.size(), value, fmt);
 }
+#endif
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 boost::charconv::from_chars_result boost::charconv::from_chars(boost::core::string_view sv, __float128& value, boost::charconv::chars_format fmt) noexcept
-- 
2.45.2