diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -4447,8 +4447,8 @@
 template <class _CharT, class _Allocator>
 struct __string_hash : public __unary_function<basic_string<_CharT, char_traits<_CharT>, _Allocator>, size_t>
 {
-    size_t
-    operator()(const basic_string<_CharT, char_traits<_CharT>, _Allocator>& __val) const _NOEXCEPT
+    _LIBCPP_HIDE_FROM_ABI
+    size_t operator()(const basic_string<_CharT, char_traits<_CharT>, _Allocator>& __val) const _NOEXCEPT
     { return std::__do_string_hash(__val.data(), __val.data() + __val.size()); }
 };