Index: libcxx/include/functional
===================================================================
--- libcxx/include/functional
+++ libcxx/include/functional
@@ -470,6 +470,7 @@
 template <> struct hash<char>;
 template <> struct hash<signed char>;
 template <> struct hash<unsigned char>;
+template <> struct hash<char8_t>; // since C++20
 template <> struct hash<char16_t>;
 template <> struct hash<char32_t>;
 template <> struct hash<wchar_t>;
Index: libcxx/include/utility
===================================================================
--- libcxx/include/utility
+++ libcxx/include/utility
@@ -1364,6 +1364,16 @@
     size_t operator()(unsigned char __v) const _NOEXCEPT {return static_cast<size_t>(__v);}
 };

+#ifndef _LIBCPP_NO_HAS_CHAR8_T
+template <>
+struct _LIBCPP_TEMPLATE_VIS hash<char8_t>
+    : public unary_function<char8_t, size_t>
+{
+    _LIBCPP_INLINE_VISIBILITY
+    size_t operator()(char8_t __v) const _NOEXCEPT {return static_cast<size_t>(__v);}
+};
+#endif // !_LIBCPP_NO_HAS_CHAR8_T
+
 #ifndef _LIBCPP_HAS_NO_UNICODE_CHARS

 template <>
Index: libcxx/test/libcxx/extensions/hash/specializations.pass.cpp
===================================================================
--- libcxx/test/libcxx/extensions/hash/specializations.pass.cpp
+++ libcxx/test/libcxx/extensions/hash/specializations.pass.cpp
@@ -23,6 +23,9 @@
     assert(__gnu_cxx::hash<char>()(42) == 42);
     assert(__gnu_cxx::hash<signed char>()(42) == 42);
     assert(__gnu_cxx::hash<unsigned char>()(42) == 42);
+    #ifdef __cpp_lib_char8_t && __cpp_lib_char8_t >= 201907L
+    assert(__gnu_cxx::hash<char8_t>()(42) == 42);
+    #endif // __cpp_lib_char8_t
     assert(__gnu_cxx::hash<short>()(42) == 42);
     assert(__gnu_cxx::hash<unsigned short>()(42) == 42);
     assert(__gnu_cxx::hash<int>()(42) == 42);