diff --git a/libcxx/include/__iterator/advance.h b/libcxx/include/__iterator/advance.h
--- a/libcxx/include/__iterator/advance.h
+++ b/libcxx/include/__iterator/advance.h
@@ -67,10 +67,12 @@
 
 #if !defined(_LIBCPP_HAS_NO_RANGES)
 
-namespace ranges {
 // [range.iter.op.advance]
-// TODO(varconst): rename `__advance_fn` to `__fn`.
-struct __advance_fn final : private __function_like {
+
+namespace ranges {
+namespace __advance {
+
+struct __fn final : private __function_like {
 private:
   template <class _Tp>
   _LIBCPP_HIDE_FROM_ABI
@@ -97,7 +99,7 @@
   }
 
 public:
-  constexpr explicit __advance_fn(__tag __x) noexcept : __function_like(__x) {}
+  constexpr explicit __fn(__tag __x) noexcept : __function_like(__x) {}
 
   // Preconditions: If `I` does not model `bidirectional_iterator`, `n` is not negative.
   template <input_or_output_iterator _Ip>
@@ -186,7 +188,11 @@
   }
 };
 
-inline constexpr auto advance = __advance_fn(__function_like::__tag());
+} // namespace __advance
+
+inline namespace __cpo {
+  inline constexpr auto advance = __advance::__fn(__function_like::__tag());
+} // namespace __cpo
 } // namespace ranges
 
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
diff --git a/libcxx/include/__iterator/next.h b/libcxx/include/__iterator/next.h
--- a/libcxx/include/__iterator/next.h
+++ b/libcxx/include/__iterator/next.h
@@ -38,11 +38,14 @@
 
 #if !defined(_LIBCPP_HAS_NO_RANGES)
 
+// [range.iter.op.next]
+
 namespace ranges {
-// TODO(varconst): rename `__next_fn` to `__fn`.
-struct __next_fn final : private __function_like {
+namespace __next {
+
+struct __fn final : private __function_like {
   _LIBCPP_HIDE_FROM_ABI
-  constexpr explicit __next_fn(__tag __x) noexcept : __function_like(__x) {}
+  constexpr explicit __fn(__tag __x) noexcept : __function_like(__x) {}
 
   template <input_or_output_iterator _Ip>
   _LIBCPP_HIDE_FROM_ABI
@@ -73,7 +76,11 @@
   }
 };
 
-inline constexpr auto next = __next_fn(__function_like::__tag());
+} // namespace __next
+
+inline namespace __cpo {
+  inline constexpr auto next = __next::__fn(__function_like::__tag());
+} // namespace __cpo
 } // namespace ranges
 
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
diff --git a/libcxx/include/__iterator/prev.h b/libcxx/include/__iterator/prev.h
--- a/libcxx/include/__iterator/prev.h
+++ b/libcxx/include/__iterator/prev.h
@@ -37,11 +37,14 @@
 
 #if !defined(_LIBCPP_HAS_NO_RANGES)
 
+// [range.iter.op.prev]
+
 namespace ranges {
-// TODO(varconst): rename `__prev_fn` to `__fn`.
-struct __prev_fn final : private __function_like {
+namespace __prev {
+
+struct __fn final : private __function_like {
   _LIBCPP_HIDE_FROM_ABI
-  constexpr explicit __prev_fn(__tag __x) noexcept : __function_like(__x) {}
+  constexpr explicit __fn(__tag __x) noexcept : __function_like(__x) {}
 
   template <bidirectional_iterator _Ip>
   _LIBCPP_HIDE_FROM_ABI
@@ -65,7 +68,11 @@
   }
 };
 
-inline constexpr auto prev = __prev_fn(__function_like::__tag());
+} // namespace __prev
+
+inline namespace __cpo {
+  inline constexpr auto prev = __prev::__fn(__function_like::__tag());
+} // namespace __cpo
 } // namespace ranges
 
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)