diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index 88c599cc..9ffcc836 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -28,7 +28,6 @@
 #endif
 
 #include "format.h"
-#include "locale.h"
 
 FMT_BEGIN_NAMESPACE
 template <typename Locale> typename Locale::id num_format_facet<Locale>::id;
@@ -120,24 +119,18 @@ template <typename Char> FMT_FUNC Char decimal_point_impl(locale_ref) {
 }
 #endif
 
-template <typename Char>
-FMT_FUNC auto write_int(unsigned long long value, locale_ref loc)
-    -> std::basic_string<Char> {
+FMT_FUNC auto write_int(unsigned long long value, const format_specs& specs,
+                        locale_ref loc) -> std::string {
 #ifndef FMT_STATIC_THOUSANDS_SEPARATOR
-  auto&& ios = std::basic_ios<Char>(nullptr);
   auto locale = loc.get<std::locale>();
-  ios.imbue(locale);
-  auto&& buf = std::basic_stringbuf<Char>();
-  auto out = std::ostreambuf_iterator<Char>(&buf);
   // We cannot use the num_put<char> facet because it may produce output in
   // a wrong encoding.
-  using facet_t =
-      conditional_t<std::is_same<Char, char>::value,
-                    num_format_facet<std::locale>, std::num_put<Char>>;
-  if (std::has_facet<facet_t>(locale)) {
-    std::use_facet<facet_t>(locale).put(out, ios, ' ', value);
-    return buf.str();
-  }
+  if (!std::has_facet<num_format_facet<std::locale>>(locale)) return {};
+  auto&& buf = std::basic_stringbuf<char>();
+  auto out = std::ostreambuf_iterator<char>(&buf);
+  std::use_facet<num_format_facet<std::locale>>(locale).put(out, value, specs,
+                                                            locale);
+  return buf.str();
 #endif
   return {};
 }
diff --git a/include/fmt/format.h b/include/fmt/format.h
index f7263354..d31d1242 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -706,6 +706,7 @@ FMT_CONSTEXPR inline size_t compute_width(string_view s) {
       return true;
     }
   };
+  // We could avoid branches by using utf8_decode directly.
   for_each_codepoint(s, count_code_points{&num_code_points});
   return num_code_points;
 }
@@ -2013,18 +2014,20 @@ auto write_int(OutputIt out, UInt value, unsigned prefix,
       });
 }
 
+FMT_API auto write_int(unsigned long long value, const format_specs& specs,
+                       locale_ref loc) -> std::string;
 template <typename Char>
-FMT_API auto write_int(unsigned long long value, locale_ref loc)
-    -> std::basic_string<Char>;
+inline auto write_int(unsigned long long, const basic_format_specs<Char>&,
+                      locale_ref) -> std::string {
+  return {};
+}
 
 template <typename OutputIt, typename UInt, typename Char>
 auto write_int(OutputIt& out, UInt value, unsigned prefix,
                const basic_format_specs<Char>& specs, locale_ref loc) -> bool {
-  using char_t =
-      conditional_t<std::is_same<Char, wchar_t>::value, wchar_t, char>;
-  auto str = std::basic_string<char_t>();
+  auto str = std::string();
   if (sizeof(value) <= sizeof(unsigned long long))
-    str = write_int<char_t>(static_cast<unsigned long long>(value), loc);
+    str = write_int(static_cast<unsigned long long>(value), specs, loc);
   if (str.empty()) {
     auto grouping = digit_grouping<Char>(loc);
     out = write_int(out, value, prefix, specs, grouping);
@@ -4171,6 +4174,25 @@ extern template FMT_API auto decimal_point_impl(locale_ref) -> wchar_t;
 
 FMT_END_DETAIL_NAMESPACE
 
+// A locale facet that formats numeric values in UTF-8.
+// It is parameterized on the locale to avoid heavy <locale> include.
+template <typename Locale> class num_format_facet : public Locale::facet {
+ public:
+  static FMT_API typename Locale::id id;
+
+  using iter_type = std::ostreambuf_iterator<char>;
+
+  auto put(iter_type out, unsigned long long val, const format_specs& specs,
+           Locale& loc) const -> iter_type {
+    return do_put(out, val, specs, loc);
+  }
+
+ protected:
+  virtual auto do_put(iter_type out, unsigned long long val,
+                      const format_specs& specs, Locale& loc) const
+      -> iter_type = 0;
+};
+
 #if FMT_USE_USER_DEFINED_LITERALS
 inline namespace literals {
 /**
diff --git a/include/fmt/locale.h b/include/fmt/locale.h
deleted file mode 100644
index cc252368..00000000
--- a/include/fmt/locale.h
+++ /dev/null
@@ -1,37 +0,0 @@
-// Formatting library for C++ - optional locale support
-//
-// Copyright (c) 2012 - present, Victor Zverovich
-// All rights reserved.
-//
-// For the license information refer to format.h.
-
-#ifndef FMT_LOCALE_H_
-#define FMT_LOCALE_H_
-
-#include <ios>       // std::ios_base
-#include <iterator>  // std::ostreambuf_iterator
-
-#include "core.h"
-
-FMT_BEGIN_NAMESPACE
-
-// A locale facet that formats numeric values in UTF-8.
-template <typename Locale> class num_format_facet : public Locale::facet {
- public:
-  static FMT_API typename Locale::id id;
-
-  using iter_type = std::ostreambuf_iterator<char>;
-
-  auto put(iter_type out, std::ios_base& str, char fill,
-           unsigned long long val) const -> iter_type {
-    return do_put(out, str, fill, val);
-  }
-
- protected:
-  virtual auto do_put(iter_type out, std::ios_base& str, char fill,
-                      unsigned long long val) const -> iter_type = 0;
-};
-
-FMT_END_NAMESPACE
-
-#endif  // FMT_LOCALE_H_
\ No newline at end of file
diff --git a/src/format.cc b/src/format.cc
index d0a7317f..19dff444 100644
--- a/src/format.cc
+++ b/src/format.cc
@@ -22,9 +22,6 @@ template FMT_API auto locale_ref::get<std::locale>() const -> std::locale;
 
 // Explicit instantiations for char.
 
-template FMT_API auto write_int(unsigned long long, locale_ref)
-    -> std::basic_string<char>;
-
 template FMT_API auto thousands_sep_impl(locale_ref)
     -> thousands_sep_result<char>;
 template FMT_API auto decimal_point_impl(locale_ref) -> char;
@@ -37,9 +34,6 @@ template FMT_API void vformat_to(buffer<char>&, string_view,
 
 // Explicit instantiations for wchar_t.
 
-template FMT_API auto write_int(unsigned long long, locale_ref)
-    -> std::basic_string<wchar_t>;
-
 template FMT_API auto thousands_sep_impl(locale_ref)
     -> thousands_sep_result<wchar_t>;
 template FMT_API auto decimal_point_impl(locale_ref) -> wchar_t;
diff --git a/test/xchar-test.cc b/test/xchar-test.cc
index 582b3495..e1958315 100644
--- a/test/xchar-test.cc
+++ b/test/xchar-test.cc
@@ -14,7 +14,6 @@
 
 #include "fmt/chrono.h"
 #include "fmt/color.h"
-#include "fmt/locale.h"
 #include "fmt/ostream.h"
 #include "fmt/ranges.h"
 #include "gtest-extra.h"  // Contains
@@ -523,13 +522,13 @@ TEST(locale_test, sign) {
 
 class num_format : public fmt::num_format_facet<std::locale> {
  protected:
-  using fmt::num_format_facet<std::locale>::do_put;
-  iter_type do_put(iter_type out, std::ios_base&, char,
-                   unsigned long long) const override;
+  iter_type do_put(iter_type out, unsigned long long, const fmt::format_specs&,
+                   std::locale&) const override;
 };
 
-num_format::iter_type num_format::do_put(iter_type out, std::ios_base&, char,
-                                         unsigned long long) const {
+num_format::iter_type num_format::do_put(iter_type out, unsigned long long,
+                                         const fmt::format_specs&,
+                                         std::locale&) const {
   const char s[] = "foo";
   return std::copy_n(s, sizeof(s) - 1, out);
 }