diff --git a/include/fmt/os.h b/include/fmt/os.h
index d82be1125a4b..8e697ec4e6fa 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -120,24 +120,6 @@ template <typename Char> class basic_cstring_view {
 using cstring_view = basic_cstring_view<char>;
 using wcstring_view = basic_cstring_view<wchar_t>;
 
-template <typename Char> struct formatter<std::error_code, Char> {
-  template <typename ParseContext>
-  FMT_CONSTEXPR auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
-    return ctx.begin();
-  }
-
-  template <typename FormatContext>
-  FMT_CONSTEXPR auto format(const std::error_code& ec, FormatContext& ctx) const
-      -> decltype(ctx.out()) {
-    auto out = ctx.out();
-    out = detail::write_bytes(out, ec.category().name(),
-                              basic_format_specs<Char>());
-    out = detail::write<Char>(out, Char(':'));
-    out = detail::write<Char>(out, ec.value());
-    return out;
-  }
-};
-
 #ifdef _WIN32
 FMT_API const std::error_category& system_category() noexcept;
 
diff --git a/include/fmt/std.h b/include/fmt/std.h
index 2896e82a0c12..ec7abaa99f05 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -180,6 +180,25 @@ FMT_END_NAMESPACE
 #endif  // __cpp_lib_variant
 
 FMT_BEGIN_NAMESPACE
+
+template <typename Char> struct formatter<std::error_code, Char> {
+  template <typename ParseContext>
+  FMT_CONSTEXPR auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
+    return ctx.begin();
+  }
+
+  template <typename FormatContext>
+  FMT_CONSTEXPR auto format(const std::error_code& ec, FormatContext& ctx) const
+      -> decltype(ctx.out()) {
+    auto out = ctx.out();
+    out = detail::write_bytes(out, ec.category().name(),
+                              basic_format_specs<Char>());
+    out = detail::write<Char>(out, Char(':'));
+    out = detail::write<Char>(out, ec.value());
+    return out;
+  }
+};
+
 template <typename T, typename Char>
 struct formatter<
     T, Char,
diff --git a/test/os-test.cc b/test/os-test.cc
index a1745c8c89ee..d93c553dc6b9 100644
--- a/test/os-test.cc
+++ b/test/os-test.cc
@@ -64,18 +64,6 @@ TEST(util_test, utf16_to_utf8_convert) {
             u.convert(wstring_view(L"foo", INT_MAX + 1u)));
 }
 
-TEST(os_test, format_std_error_code) {
-  EXPECT_EQ("generic:42",
-            fmt::format(FMT_STRING("{0}"),
-                        std::error_code(42, std::generic_category())));
-  EXPECT_EQ("system:42",
-            fmt::format(FMT_STRING("{0}"),
-                        std::error_code(42, fmt::system_category())));
-  EXPECT_EQ("system:-42",
-            fmt::format(FMT_STRING("{0}"),
-                        std::error_code(-42, fmt::system_category())));
-}
-
 TEST(os_test, format_windows_error) {
   LPWSTR message = nullptr;
   auto result = FormatMessageW(
diff --git a/test/std-test.cc b/test/std-test.cc
index f700a510f74b..4411d3d1cd39 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -10,6 +10,7 @@
 #include <string>
 #include <vector>
 
+#include "fmt/os.h"  // fmt::system_category
 #include "fmt/ranges.h"
 #include "gtest-extra.h"  // StartsWith
 
@@ -83,6 +84,18 @@ TEST(std_test, variant) {
 #endif
 }
 
+TEST(std_test, error_code) {
+  EXPECT_EQ("generic:42",
+            fmt::format(FMT_STRING("{0}"),
+                        std::error_code(42, std::generic_category())));
+  EXPECT_EQ("system:42",
+            fmt::format(FMT_STRING("{0}"),
+                        std::error_code(42, fmt::system_category())));
+  EXPECT_EQ("system:-42",
+            fmt::format(FMT_STRING("{0}"),
+                        std::error_code(-42, fmt::system_category())));
+}
+
 template <typename Catch> void exception_test() {
   try {
     throw std::runtime_error("Test Exception");