diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index 61c910c52c536..fe0f46c876f5e 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -1165,32 +1165,81 @@ public:
   template <class _Key>
   _LIBCPP_HIDE_FROM_ABI size_type __count_multi(const _Key& __k) const;
 
+  template <bool _LowerBound, class _Key>
+  _LIBCPP_HIDE_FROM_ABI __end_node_pointer __lower_upper_bound_unique_impl(const _Key& __v) const {
+    auto __rt     = __root();
+    auto __result = __end_node();
+    auto __comp   = __lazy_synth_three_way_comparator<_Compare, _Key, value_type>(value_comp());
+    while (__rt != nullptr) {
+      auto __comp_res = __comp(__v, __rt->__get_value());
+
+      if (__comp_res.__less()) {
+        __result = static_cast<__end_node_pointer>(__rt);
+        __rt     = static_cast<__node_pointer>(__rt->__left_);
+      } else if (__comp_res.__greater()) {
+        __rt = static_cast<__node_pointer>(__rt->__right_);
+      } else if _LIBCPP_CONSTEXPR (_LowerBound) {
+        return static_cast<__end_node_pointer>(__rt);
+      } else {
+        return __rt->__right_ ? static_cast<__end_node_pointer>(std::__tree_min(__rt->__right_)) : __result;
+      }
+    }
+    return __result;
+  }
+
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _Key& __v) {
-    return __lower_bound(__v, __root(), __end_node());
+  _LIBCPP_HIDE_FROM_ABI iterator __lower_bound_unique(const _Key& __v) {
+    return iterator(__lower_upper_bound_unique_impl<true>(__v));
   }
+
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI iterator __lower_bound(const _Key& __v, __node_pointer __root, __end_node_pointer __result);
+  _LIBCPP_HIDE_FROM_ABI const_iterator __lower_bound_unique(const _Key& __v) const {
+    return const_iterator(__lower_upper_bound_unique_impl<true>(__v));
+  }
+
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _Key& __v) const {
-    return __lower_bound(__v, __root(), __end_node());
+  _LIBCPP_HIDE_FROM_ABI iterator __upper_bound_unique(const _Key& __v) {
+    return iterator(__lower_upper_bound_unique_impl<false>(__v));
+  }
+
+  template <class _Key>
+  _LIBCPP_HIDE_FROM_ABI const_iterator __upper_bound_unique(const _Key& __v) const {
+    return iterator(__lower_upper_bound_unique_impl<false>(__v));
   }
+
+  template <class _Key>
+  _LIBCPP_HIDE_FROM_ABI iterator __lower_bound(const _Key& __v, __node_pointer __root, __end_node_pointer __result);
+
   template <class _Key>
   _LIBCPP_HIDE_FROM_ABI const_iterator
   __lower_bound(const _Key& __v, __node_pointer __root, __end_node_pointer __result) const;
+
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _Key& __v) {
-    return __upper_bound(__v, __root(), __end_node());
+  _LIBCPP_HIDE_FROM_ABI iterator __lower_bound_multi(const _Key& __v) {
+    return __lower_bound(__v, __root(), __end_node());
   }
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI iterator __upper_bound(const _Key& __v, __node_pointer __root, __end_node_pointer __result);
+  _LIBCPP_HIDE_FROM_ABI const_iterator __lower_bound_multi(const _Key& __v) const {
+    return __lower_bound(__v, __root(), __end_node());
+  }
+
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _Key& __v) const {
+  _LIBCPP_HIDE_FROM_ABI iterator __upper_bound_multi(const _Key& __v) {
     return __upper_bound(__v, __root(), __end_node());
   }
+
+  template <class _Key>
+  _LIBCPP_HIDE_FROM_ABI const_iterator __upper_bound_multi(const _Key& __v) const {
+    return __upper_bound(__v, __root(), __end_node());
+  }
+
+  template <class _Key>
+  _LIBCPP_HIDE_FROM_ABI iterator __upper_bound(const _Key& __v, __node_pointer __root, __end_node_pointer __result);
+
   template <class _Key>
   _LIBCPP_HIDE_FROM_ABI const_iterator
   __upper_bound(const _Key& __v, __node_pointer __root, __end_node_pointer __result) const;
+
   template <class _Key>
   _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> __equal_range_unique(const _Key& __k);
   template <class _Key>
diff --git a/libcxx/include/map b/libcxx/include/map
index a63dfec910aae..37c0daaa0c2af 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -1268,30 +1268,40 @@ public:
   }
 #  endif // _LIBCPP_STD_VER >= 20
 
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.lower_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const { return __tree_.lower_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.__lower_bound_unique(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const {
+    return __tree_.__lower_bound_unique(__k);
+  }
+
+  // The transparent versions of the lookup functions use the _multi version, since a non-element key is allowed to
+  // match multiple elements.
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.upper_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const { return __tree_.upper_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.__upper_bound_unique(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const {
+    return __tree_.__upper_bound_unique(__k);
+  }
+
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
 #  endif
 
@@ -1831,30 +1841,38 @@ public:
   }
 #  endif // _LIBCPP_STD_VER >= 20
 
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.lower_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const { return __tree_.lower_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.__lower_bound_multi(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const {
+    return __tree_.__lower_bound_multi(__k);
+  }
+
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.upper_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const { return __tree_.upper_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.__upper_bound_multi(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const {
+    return __tree_.__upper_bound_multi(__k);
+  }
+
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
 #  endif
 
diff --git a/libcxx/include/set b/libcxx/include/set
index 75529e7bac6ff..661930b0a6f6c 100644
--- a/libcxx/include/set
+++ b/libcxx/include/set
@@ -849,30 +849,40 @@ public:
   }
 #  endif // _LIBCPP_STD_VER >= 20
 
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.lower_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const { return __tree_.lower_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.__lower_bound_unique(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const {
+    return __tree_.__lower_bound_unique(__k);
+  }
+
+  // The transparent versions of the lookup functions use the _multi version, since a non-element key is allowed to
+  // match multiple elements.
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.upper_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const { return __tree_.upper_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.__upper_bound_unique(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const {
+    return __tree_.__upper_bound_unique(__k);
+  }
+
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
 #  endif
 
@@ -1301,30 +1311,38 @@ public:
   }
 #  endif // _LIBCPP_STD_VER >= 20
 
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.lower_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const { return __tree_.lower_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.__lower_bound_multi(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const {
+    return __tree_.__lower_bound_multi(__k);
+  }
+
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const {
-    return __tree_.lower_bound(__k);
+    return __tree_.__lower_bound_multi(__k);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.upper_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const { return __tree_.upper_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.__upper_bound_multi(__k); }
+
+  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const {
+    return __tree_.__upper_bound_multi(__k);
+  }
+
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const {
-    return __tree_.upper_bound(__k);
+    return __tree_.__upper_bound_multi(__k);
   }
 #  endif