diff --git a/src/core-io/include/units/bits/external/fixed_string_io.h b/src/core-io/include/units/bits/external/fixed_string_io.h
deleted file mode 100644
index d06cc5cc..00000000
--- a/src/core-io/include/units/bits/external/fixed_string_io.h
+++ /dev/null
@@ -1,37 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-#include <units/bits/external/fixed_string.h>
-#include <ostream>
-
-namespace units {
-
-template<typename CharT, class Traits, std::size_t N>
-std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os,
-                                              const basic_fixed_string<CharT, N>& txt)
-{
-  return os << txt.c_str();
-}
-
-}  // namespace units
diff --git a/src/core-io/include/units/quantity_io.h b/src/core-io/include/units/quantity_io.h
index b4081ebb..8ff43e15 100644
--- a/src/core-io/include/units/quantity_io.h
+++ b/src/core-io/include/units/quantity_io.h
@@ -24,31 +24,27 @@
 #pragma once
 
 #include <units/quantity.h>
-
-// IWYU pragma: begin_exports
-#include <units/bits/external/fixed_string_io.h>
-#include <units/bits/unit_text.h>
+#include <units/unit.h>
 #include <sstream>
-// IWYU pragma: end_exports
 
 namespace units {
 
 namespace detail {
 
-template<typename CharT, class Traits, typename D, typename U, typename Rep>
-void to_stream(std::basic_ostream<CharT, Traits>& os, const quantity<D, U, Rep>& q)
+template<typename CharT, class Traits, auto R, typename Rep>
+void to_stream(std::basic_ostream<CharT, Traits>& os, const quantity<R, Rep>& q)
 {
   os << q.number();
-  constexpr auto symbol = detail::unit_text<D, U>();
-  if constexpr (!symbol.standard().empty()) {
-    os << " " << symbol.standard();
+  if constexpr (!std::derived_from<decltype(R.unit), derived_unit<>>) {
+    os << " ";
+    unit_symbol_to<CharT>(std::ostream_iterator<CharT>(os), R.unit);
   }
 }
 
 }  //  namespace detail
 
-template<typename CharT, typename Traits, typename D, typename U, typename Rep>
-std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const quantity<D, U, Rep>& q)
+template<typename CharT, typename Traits, auto R, typename Rep>
+std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const quantity<R, Rep>& q)
   requires requires { os << q.number(); }
 {
   if (os.width()) {