diff --git a/include/string b/include/string
index a456f8c..804373b 100644
--- a/include/string
+++ b/include/string
@@ -83,6 +83,7 @@ template <> struct char_traits<char32_t>;
 template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> >
 class basic_string
 {
+    static_assert(sizeof(_CharT) <= 4, "libc++ implementation of std::basic_string does not support extra-wide character types");
 public:
 // types:
     typedef traits traits_type;
@@ -981,9 +982,10 @@ 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()) {
@@ -991,6 +993,8 @@ 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) {
@@ -1155,7 +1159,7 @@ public:
   _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);
@@ -1212,6 +1216,10 @@ 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()); }
 
@@ -1759,7 +1767,7 @@ public:
   }
 #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);
   }