diff --git a/doc/api.rst b/doc/api.rst
index 07ed6d4c..2787bd1d 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -335,50 +335,6 @@ arguments, the container that stores pointers to them will be allocated using
 the default allocator. Also floating-point formatting falls back on ``sprintf``
 which may do allocations.
 
-Custom Formatting of Built-in Types
------------------------------------
-
-It is possible to change the way arguments are formatted by providing a
-custom argument formatter class::
-
-  using arg_formatter = fmt::arg_formatter<fmt::buffer_range<char>>;
-
-  // A custom argument formatter that formats negative integers as unsigned
-  // with the ``x`` format specifier.
-  class custom_arg_formatter : public arg_formatter {
-   public:
-    custom_arg_formatter(fmt::format_context& ctx,
-                         fmt::format_parse_context* parse_ctx = nullptr,
-                         fmt::format_specs* spec = nullptr)
-      : arg_formatter(ctx, parse_ctx, spec) {}
-
-    using arg_formatter::operator();
-
-    auto operator()(int value) {
-      if (specs() && specs()->type == 'x')
-        return (*this)(static_cast<unsigned>(value)); // convert to unsigned and format
-      return arg_formatter::operator()(value);
-    }
-  };
-
-  std::string custom_vformat(fmt::string_view format_str, fmt::format_args args) {
-    fmt::memory_buffer buffer;
-    // Pass custom argument formatter as a template arg to vformat_to.
-    fmt::vformat_to<custom_arg_formatter>(buffer, format_str, args);
-    return fmt::to_string(buffer);
-  }
-
-  template <typename ...Args>
-  inline std::string custom_format(
-      fmt::string_view format_str, const Args&... args) {
-    return custom_vformat(format_str, fmt::make_format_args(args...));
-  }
-
-  std::string s = custom_format("{:x}", -42); // s == "ffffffd6"
-
-.. doxygenclass:: fmt::arg_formatter
-   :members:
-
 .. _ranges-api:
 
 Ranges and Tuple Formatting
diff --git a/include/fmt/format.h b/include/fmt/format.h
index c75089d8..1c0b3840 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -566,7 +566,8 @@ template <typename U>
 void buffer<T>::append(const U* begin, const U* end) {
   size_t new_size = size_ + to_unsigned(end - begin);
   reserve(new_size);
-  std::uninitialized_copy(begin, end, make_checked(ptr_ + size_, capacity_ - size_));
+  std::uninitialized_copy(begin, end,
+                          make_checked(ptr_ + size_, capacity_ - size_));
   size_ = new_size;
 }
 }  // namespace detail
@@ -2886,14 +2887,13 @@ FMT_API void format_error_code(buffer<char>& out, int error_code,
 
 FMT_API void report_error(format_func func, int error_code,
                           string_view message) FMT_NOEXCEPT;
-}  // namespace detail
 
 /** The default argument formatter. */
 template <typename OutputIt, typename Char>
-class arg_formatter : public detail::arg_formatter_base<OutputIt, Char> {
+class arg_formatter : public arg_formatter_base<OutputIt, Char> {
  private:
   using char_type = Char;
-  using base = detail::arg_formatter_base<OutputIt, Char>;
+  using base = arg_formatter_base<OutputIt, Char>;
   using context_type = basic_format_context<OutputIt, Char>;
 
   context_type& ctx_;
@@ -2929,6 +2929,11 @@ class arg_formatter : public detail::arg_formatter_base<OutputIt, Char> {
     return ctx_.out();
   }
 };
+}  // namespace detail
+
+template <typename OutputIt, typename Char>
+using arg_formatter FMT_DEPRECATED_ALIAS =
+  detail::arg_formatter<OutputIt, Char>;
 
 /**
  An error returned by an operating system or a language runtime,
@@ -3139,8 +3144,8 @@ struct formatter<T, Char,
                                                        specs_.width_ref, ctx);
     detail::handle_dynamic_spec<detail::precision_checker>(
         specs_.precision, specs_.precision_ref, ctx);
-    using af = arg_formatter<typename FormatContext::iterator,
-                             typename FormatContext::char_type>;
+    using af = detail::arg_formatter<typename FormatContext::iterator,
+                                     typename FormatContext::char_type>;
     return visit_format_arg(af(ctx, nullptr, &specs_),
                             detail::make_arg<FormatContext>(val));
   }
@@ -3235,8 +3240,8 @@ template <typename Char = char> class dynamic_formatter {
     }
     if (specs_.alt) checker.on_hash();
     if (specs_.precision >= 0) checker.end_precision();
-    using af = arg_formatter<typename FormatContext::iterator,
-                             typename FormatContext::char_type>;
+    using af = detail::arg_formatter<typename FormatContext::iterator,
+                                     typename FormatContext::char_type>;
     visit_format_arg(af(ctx, nullptr, &specs_),
                      detail::make_arg<FormatContext>(val));
     return ctx.out();
@@ -3506,7 +3511,7 @@ template <
 inline OutputIt vformat_to(
     OutputIt out, const S& format_str,
     format_args_t<type_identity_t<OutputIt>, char_t<S>> args) {
-  using af = arg_formatter<OutputIt, char_t<S>>;
+  using af = detail::arg_formatter<OutputIt, char_t<S>>;
   return vformat_to<af>(out, to_string_view(format_str), args);
 }
 
diff --git a/include/fmt/locale.h b/include/fmt/locale.h
index dd75b45f..988d15cd 100644
--- a/include/fmt/locale.h
+++ b/include/fmt/locale.h
@@ -56,7 +56,7 @@ template <typename S, typename OutputIt, typename... Args,
 inline OutputIt vformat_to(
     OutputIt out, const std::locale& loc, const S& format_str,
     format_args_t<type_identity_t<OutputIt>, Char> args) {
-  using af = arg_formatter<OutputIt, Char>;
+  using af = detail::arg_formatter<OutputIt, Char>;
   return vformat_to<af>(out, to_string_view(format_str), args,
                         detail::locale_ref(loc));
 }
diff --git a/test/custom-formatter-test.cc b/test/custom-formatter-test.cc
index c5d748e8..1b0c1e13 100644
--- a/test/custom-formatter-test.cc
+++ b/test/custom-formatter-test.cc
@@ -18,9 +18,9 @@
 // A custom argument formatter that doesn't print `-` for floating-point values
 // rounded to 0.
 class custom_arg_formatter
-    : public fmt::arg_formatter<fmt::format_context::iterator, char> {
+    : public fmt::detail::arg_formatter<fmt::format_context::iterator, char> {
  public:
-  using base = fmt::arg_formatter<fmt::format_context::iterator, char>;
+  using base = fmt::detail::arg_formatter<fmt::format_context::iterator, char>;
 
   custom_arg_formatter(fmt::format_context& ctx,
                        fmt::format_parse_context* parse_ctx,
diff --git a/test/ostream-test.cc b/test/ostream-test.cc
index e572cf19..1c87d46d 100644
--- a/test/ostream-test.cc
+++ b/test/ostream-test.cc
@@ -65,10 +65,10 @@ TEST(OStreamTest, Enum) {
 }
 
 struct test_arg_formatter
-    : fmt::arg_formatter<fmt::format_context::iterator, char> {
+    : fmt::detail::arg_formatter<fmt::format_context::iterator, char> {
   fmt::format_parse_context parse_ctx;
   test_arg_formatter(fmt::format_context& ctx, fmt::format_specs& s)
-      : fmt::arg_formatter<fmt::format_context::iterator, char>(
+      : fmt::detail::arg_formatter<fmt::format_context::iterator, char>(
             ctx, &parse_ctx, &s),
         parse_ctx("") {}
 };