diff --git a/include/math.h b/include/math.h
index 5bde46a..33bf0eb 100644
--- a/include/math.h
+++ b/include/math.h
@@ -326,7 +326,7 @@ extern "C++" {
 #      undef isinf
 #    endif
 
-#    ifdef isnan
+#    if defined(isnan) && !defined(_LIBCPP_MSVCRT)
 #      undef isnan
 #    endif
 
diff --git a/include/string b/include/string
index 123e1d6..57624c7 100644
--- a/include/string
+++ b/include/string
@@ -703,6 +703,7 @@ struct __init_with_sentinel_tag {};
 template<class _CharT, class _Traits, class _Allocator>
 class basic_string
 {
+    static_assert(sizeof(_CharT) <= 4, "libc++ implementation of std::basic_string does not support extra-wide character types");
 public:
     typedef basic_string                                 __self;
     typedef basic_string_view<_CharT, _Traits>           __self_view;
@@ -947,9 +948,11 @@ public:
     __init(__s, traits_type::length(__s));
   }
 
-#if _LIBCPP_STD_VER >= 23
+#if _LIBCPP_STD_VER >= 20
   basic_string(nullptr_t) = delete;
 #endif
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+  basic_string(nullptr_t, size_t) = delete;
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* __s, size_type __n)
       : __r_(__default_init_tag(), __default_init_tag()) {
@@ -957,6 +960,9 @@ public:
     __init(__s, __n);
   }
 
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+  basic_string(nullptr_t, size_t, const _Allocator&) = delete;
+
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
   basic_string(const _CharT* __s, size_type __n, const _Allocator& __a)
       : __r_(__default_init_tag(), __a) {
@@ -1120,7 +1126,7 @@ public:
 #endif
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     basic_string& operator=(const value_type* __s) {return assign(__s);}
-#if _LIBCPP_STD_VER >= 23
+#if _LIBCPP_STD_VER >= 20
     basic_string& operator=(nullptr_t) = delete;
 #endif
     _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& operator=(value_type __c);
@@ -1182,6 +1188,13 @@ public:
         return (__is_long() ? __get_long_cap() : static_cast<size_type>(__min_cap)) - 1;
     }
 
+#if _YNDX_LIBCXX_ENABLE_STRING_RESIZE_UNINITIALIZED == 1
+    inline void resize_uninitialized(size_type __n)
+    {
+        __resize_default_init(__n);
+    }
+#endif
+
     _LIBCPP_CONSTEXPR_SINCE_CXX20 void resize(size_type __n, value_type __c);
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void resize(size_type __n) { resize(__n, value_type()); }
 
@@ -1701,7 +1714,7 @@ public:
     { return ends_with(__self_view(__s)); }
 #endif
 
-#if _LIBCPP_STD_VER >= 23
+#if _LIBCPP_STD_VER >= 20
     constexpr _LIBCPP_HIDE_FROM_ABI
     bool contains(__self_view __sv) const noexcept
     { return __self_view(data(), size()).contains(__sv); }