diff --git a/docs/users_guide/examples/hello_units.md b/docs/users_guide/examples/hello_units.md
index c77f2287..c33e9034 100644
--- a/docs/users_guide/examples/hello_units.md
+++ b/docs/users_guide/examples/hello_units.md
@@ -18,20 +18,20 @@ First, we either import the `mp_units` module or include the headers for:
 - text formatting and stream output support
 
 ```cpp title="hello_units.cpp" linenums="1"
---8<-- "example/hello_units.cpp:28:40"
+--8<-- "example/hello_units.cpp:28:41"
 ```
 
 Also, to shorten the definitions, we "import" all the symbols from the `mp_units` namespace.
 
-```cpp title="hello_units.cpp" linenums="13"
---8<-- "example/hello_units.cpp:41:42"
+```cpp title="hello_units.cpp" linenums="14"
+--8<-- "example/hello_units.cpp:42:43"
 ```
 
 Next, we define a simple function that calculates the average speed based on the provided
 arguments of length and time:
 
-```cpp title="hello_units.cpp" linenums="14"
---8<-- "example/hello_units.cpp:43:46"
+```cpp title="hello_units.cpp" linenums="15"
+--8<-- "example/hello_units.cpp:44:47"
 ```
 
 The above function template takes any quantities implicitly convertible to `isq::length`
@@ -45,37 +45,37 @@ that its quantity type is implicitly convertible to `isq::speed`.
     type is beneficial for users of such a function as it provides more information
     of what to expect from a function than just using `auto`.
 
-```cpp title="hello_units.cpp" linenums="18"
---8<-- "example/hello_units.cpp:48:51"
+```cpp title="hello_units.cpp" linenums="19"
+--8<-- "example/hello_units.cpp:49:52"
 ```
 
 The above lines explicitly opt into using unit symbols from two systems of units.
 As this introduces a lot of short identifiers into the current scope, it is not done
 implicitly while including a header file.
 
-```cpp title="hello_units.cpp" linenums="22"
---8<-- "example/hello_units.cpp:53:59"
+```cpp title="hello_units.cpp" linenums="23"
+--8<-- "example/hello_units.cpp:54:60"
 ```
 
-- Lines `21` & `22` create a quantity of kind `isq::length / isq::time` with the numbers
+- Lines `23` & `24` create a quantity of kind `isq::length / isq::time` with the numbers
   and units provided. Such quantities can be converted or assigned to any other quantity
   with a matching kind.
-- Line `23` calls our function template with quantities of kind `isq::length` and
+- Line `25` calls our function template with quantities of kind `isq::length` and
   `isq::time` and number and units provided.
-- Line `24` explicitly provides quantity types of the quantities passed to a function template.
+- Line `26` explicitly provides quantity types of the quantities passed to a function template.
   This time, those will not be quantity kinds anymore and will have
   [more restrictive conversion rules](../framework_basics/simple_and_typed_quantities.md#quantity_cast-to-force-unsafe-conversions).
-- Line `25` changes the unit of a quantity `v3` to `m / s` in a
+- Line `27` changes the unit of a quantity `v3` to `m / s` in a
   [value-preserving way](../framework_basics/value_conversions.md#value-preserving-conversions)
   (floating-point representations are considered to be value-preserving).
-- Line `26` does a similar operation, but this time, it would also succeed for
+- Line `28` does a similar operation, but this time, it would also succeed for
   [value-truncating cases](../framework_basics/value_conversions.md#value-truncating-conversions)
   (if that was the case).
-- Line `27` does a [value-truncating conversion](../framework_basics/value_conversions.md#value-truncating-conversions)
+- Line `29` does a [value-truncating conversion](../framework_basics/value_conversions.md#value-truncating-conversions)
   of changing the underlying representation type from `double` to `int`.
 
-```cpp title="hello_units.cpp" linenums="29"
---8<-- "example/hello_units.cpp:61"
+```cpp title="hello_units.cpp" linenums="30"
+--8<-- "example/hello_units.cpp:62"
 ```
 
 The above presents [various ways to print a quantity](../framework_basics/text_output.md).
diff --git a/docs/users_guide/examples/si_constants.md b/docs/users_guide/examples/si_constants.md
index ab331bc6..0a2f5496 100644
--- a/docs/users_guide/examples/si_constants.md
+++ b/docs/users_guide/examples/si_constants.md
@@ -13,7 +13,7 @@ how [Faster-than-lightspeed Constants](../framework_basics/faster_than_lightspee
 work in practice.
 
 ```cpp title="si_constants.cpp" linenums="1"
---8<-- "example/si_constants.cpp:28:39"
+--8<-- "example/si_constants.cpp:28:40"
 ```
 
 As always, we start with the inclusion of all the needed header files. After that, for
@@ -21,8 +21,8 @@ the simplicity of this example, we
 [hack the character of quantities](../framework_basics/character_of_a_quantity.md#hacking-the-character)
 to be able to express vector quantities with simple scalar types.
 
-```cpp title="si_constants.cpp" linenums="13"
---8<-- "example/si_constants.cpp:41:"
+```cpp title="si_constants.cpp" linenums="14"
+--8<-- "example/si_constants.cpp:42:"
 ```
 
 The main part of the example prints all of the SI-defining constants. While analyzing the output of
diff --git a/docs/users_guide/use_cases/wide_compatibility.md b/docs/users_guide/use_cases/wide_compatibility.md
index b8e7d465..c8aa6211 100644
--- a/docs/users_guide/use_cases/wide_compatibility.md
+++ b/docs/users_guide/use_cases/wide_compatibility.md
@@ -96,6 +96,7 @@ your code using **mp-units**:
 
     ```cpp
     #include <iostream>
+    #include <mp-units/ext/format.h>
     #ifdef MP_UNITS_MODULES
     #include <mp-units/compat_macros.h>
     import mp_units;
@@ -158,6 +159,13 @@ This macro resolves to either the `std` or `fmt` namespace, depending on the val
 [MP_UNITS_API_STD_FORMAT](../../getting_started/installation_and_usage.md#MP_UNITS_API_STD_FORMAT)
 CMake option.
 
+To include the header files of the underlying text formatting framework, the following include
+should be used:
+
+```cpp
+#include <mp-units/ext/format.h>
+```
+
 ### Contracts
 
 The mp-units library internally does contract checking by default. It can be disabled with a Conan
diff --git a/example/clcpp_response.cpp b/example/clcpp_response.cpp
index dbdca1e3..a1f252ad 100644
--- a/example/clcpp_response.cpp
+++ b/example/clcpp_response.cpp
@@ -16,6 +16,7 @@
 */
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
 import mp_units;
diff --git a/example/conversion_factor.cpp b/example/conversion_factor.cpp
index b95c018e..cc5ff291 100644
--- a/example/conversion_factor.cpp
+++ b/example/conversion_factor.cpp
@@ -16,6 +16,7 @@
 */
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <concepts>
 #include <iostream>
 #include <string>
diff --git a/example/foot_pound_second.cpp b/example/foot_pound_second.cpp
index f62804f5..2bb1e7d0 100644
--- a/example/foot_pound_second.cpp
+++ b/example/foot_pound_second.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <iostream>
 #include <string>
 #include <string_view>
diff --git a/example/glide_computer.cpp b/example/glide_computer.cpp
index 4da86872..e263d149 100644
--- a/example/glide_computer.cpp
+++ b/example/glide_computer.cpp
@@ -24,6 +24,7 @@
 #include "glide_computer_lib.h"
 #include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <array>
 #include <chrono>
 #include <concepts>
diff --git a/example/glide_computer_lib/glide_computer_lib.cpp b/example/glide_computer_lib/glide_computer_lib.cpp
index 7c144939..6342a905 100644
--- a/example/glide_computer_lib/glide_computer_lib.cpp
+++ b/example/glide_computer_lib/glide_computer_lib.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include "glide_computer_lib.h"
+#include <mp-units/ext/format.h>
 #include <functional>
 #include <iostream>
 #include <numeric>
diff --git a/example/hello_units.cpp b/example/hello_units.cpp
index 283b223e..f11f8a3a 100644
--- a/example/hello_units.cpp
+++ b/example/hello_units.cpp
@@ -26,6 +26,7 @@
 // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <iomanip>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
diff --git a/example/include/geographic.h b/example/include/geographic.h
index 5366303c..53e086e3 100644
--- a/example/include/geographic.h
+++ b/example/include/geographic.h
@@ -24,6 +24,7 @@
 
 #include "ranged_representation.h"
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <compare>
 #include <limits>
 #include <numbers>
diff --git a/example/include/ranged_representation.h b/example/include/ranged_representation.h
index 9fc493cd..350a3b04 100644
--- a/example/include/ranged_representation.h
+++ b/example/include/ranged_representation.h
@@ -25,6 +25,7 @@
 #include "validated_type.h"
 #include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <algorithm>
 #include <concepts>
 #include <type_traits>
diff --git a/example/include/validated_type.h b/example/include/validated_type.h
index a0a7b91c..30722c50 100644
--- a/example/include/validated_type.h
+++ b/example/include/validated_type.h
@@ -25,6 +25,7 @@
 #include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
 #include <mp-units/ext/contracts.h>
+#include <mp-units/ext/format.h>
 #include <compare>  // IWYU pragma: export
 #include <ostream>
 #include <utility>
diff --git a/example/kalman_filter/kalman.h b/example/kalman_filter/kalman.h
index 86659065..501dd2cc 100644
--- a/example/kalman_filter/kalman.h
+++ b/example/kalman_filter/kalman.h
@@ -23,6 +23,7 @@
 #pragma once
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <algorithm>
 #include <locale>
 #include <tuple>
diff --git a/example/kalman_filter/kalman_filter-example_1.cpp b/example/kalman_filter/kalman_filter-example_1.cpp
index a5f8778a..7bfb370a 100644
--- a/example/kalman_filter/kalman_filter-example_1.cpp
+++ b/example/kalman_filter/kalman_filter-example_1.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <mp-units/ext/format.h>
 #include <array>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
diff --git a/example/kalman_filter/kalman_filter-example_2.cpp b/example/kalman_filter/kalman_filter-example_2.cpp
index d9fab7f9..f1fffedd 100644
--- a/example/kalman_filter/kalman_filter-example_2.cpp
+++ b/example/kalman_filter/kalman_filter-example_2.cpp
@@ -23,6 +23,7 @@
 #include "kalman.h"
 #include <array>
 #include <iostream>
+#include <mp-units/ext/format.h>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
diff --git a/example/kalman_filter/kalman_filter-example_3.cpp b/example/kalman_filter/kalman_filter-example_3.cpp
index 931cba60..a69c39e6 100644
--- a/example/kalman_filter/kalman_filter-example_3.cpp
+++ b/example/kalman_filter/kalman_filter-example_3.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <mp-units/ext/format.h>
 #include <array>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
diff --git a/example/kalman_filter/kalman_filter-example_4.cpp b/example/kalman_filter/kalman_filter-example_4.cpp
index 073bc4a1..b04ae971 100644
--- a/example/kalman_filter/kalman_filter-example_4.cpp
+++ b/example/kalman_filter/kalman_filter-example_4.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <mp-units/ext/format.h>
 #include <array>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
diff --git a/example/kalman_filter/kalman_filter-example_5.cpp b/example/kalman_filter/kalman_filter-example_5.cpp
index 8a594ded..d12a22fe 100644
--- a/example/kalman_filter/kalman_filter-example_5.cpp
+++ b/example/kalman_filter/kalman_filter-example_5.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <mp-units/ext/format.h>
 #include <array>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
diff --git a/example/kalman_filter/kalman_filter-example_6.cpp b/example/kalman_filter/kalman_filter-example_6.cpp
index 96cc1d38..7e17b23c 100644
--- a/example/kalman_filter/kalman_filter-example_6.cpp
+++ b/example/kalman_filter/kalman_filter-example_6.cpp
@@ -23,6 +23,7 @@
 #include "kalman.h"
 #include <array>
 #include <iostream>
+#include <mp-units/ext/format.h>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
diff --git a/example/kalman_filter/kalman_filter-example_7.cpp b/example/kalman_filter/kalman_filter-example_7.cpp
index ecf52f96..62ce652b 100644
--- a/example/kalman_filter/kalman_filter-example_7.cpp
+++ b/example/kalman_filter/kalman_filter-example_7.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <mp-units/ext/format.h>
 #include <array>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
diff --git a/example/kalman_filter/kalman_filter-example_8.cpp b/example/kalman_filter/kalman_filter-example_8.cpp
index e9e06da0..760212ec 100644
--- a/example/kalman_filter/kalman_filter-example_8.cpp
+++ b/example/kalman_filter/kalman_filter-example_8.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <mp-units/ext/format.h>
 #include <array>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
diff --git a/example/si_constants.cpp b/example/si_constants.cpp
index f88b08fe..56b016a8 100644
--- a/example/si_constants.cpp
+++ b/example/si_constants.cpp
@@ -26,6 +26,7 @@
 // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <iostream>
 #ifdef MP_UNITS_MODULES
 import mp_units;
diff --git a/example/spectroscopy_units.cpp b/example/spectroscopy_units.cpp
index ae12080b..e64eee8f 100644
--- a/example/spectroscopy_units.cpp
+++ b/example/spectroscopy_units.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <iostream>
 #include <tuple>
 #ifdef MP_UNITS_MODULES
diff --git a/example/storage_tank.cpp b/example/storage_tank.cpp
index 3622e081..7e004cf0 100644
--- a/example/storage_tank.cpp
+++ b/example/storage_tank.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <cassert>
 #include <chrono>
 #include <iostream>
diff --git a/example/unmanned_aerial_vehicle.cpp b/example/unmanned_aerial_vehicle.cpp
index 23b05ccf..914de0db 100644
--- a/example/unmanned_aerial_vehicle.cpp
+++ b/example/unmanned_aerial_vehicle.cpp
@@ -23,6 +23,7 @@
 #include "geographic.h"
 #include "ranged_representation.h"
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <cassert>
 #include <cstdint>
 #include <iostream>
@@ -30,6 +31,7 @@
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
+#include <mp-units/bits/fmt.h>
 #include <mp-units/systems/international.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si.h>
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 733e3586..1a48573b 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -46,6 +46,7 @@ add_mp_units_module(
             include/mp-units/ext/algorithm.h
             include/mp-units/ext/contracts.h
             include/mp-units/ext/fixed_string.h
+            include/mp-units/ext/format.h
             include/mp-units/ext/prime.h
             include/mp-units/ext/type_name.h
             include/mp-units/ext/type_traits.h
diff --git a/src/core/include/mp-units/bits/core_gmf.h b/src/core/include/mp-units/bits/core_gmf.h
index 08defcae..c920c6ae 100644
--- a/src/core/include/mp-units/bits/core_gmf.h
+++ b/src/core/include/mp-units/bits/core_gmf.h
@@ -45,23 +45,13 @@
 #include <utility>
 
 #if MP_UNITS_HOSTED
+#include <mp-units/ext/format.h>
 #include <cmath>
 #include <locale>
 #include <ostream>
 #include <random>
 #include <sstream>
 #include <string>
-
-#if MP_UNITS_USE_FMTLIB
-MP_UNITS_DIAGNOSTIC_PUSH
-MP_UNITS_DIAGNOSTIC_IGNORE_UNREACHABLE
-MP_UNITS_DIAGNOSTIC_IGNORE_SHADOW
-#include <fmt/format.h>
-MP_UNITS_DIAGNOSTIC_POP
-#else
-#include <format>
-#endif
-
 #endif
 
 #if __cpp_lib_text_encoding
diff --git a/src/core/include/mp-units/bits/fmt.h b/src/core/include/mp-units/bits/fmt.h
index bc3197e0..610be604 100644
--- a/src/core/include/mp-units/bits/fmt.h
+++ b/src/core/include/mp-units/bits/fmt.h
@@ -41,6 +41,7 @@
 #include <limits>
 #include <string_view>
 #include <mp-units/ext/contracts.h>
+#include <mp-units/ext/format.h>
 #endif
 
 // most of the below code is based on/copied from fmtlib
diff --git a/src/core/include/mp-units/compat_macros.h b/src/core/include/mp-units/compat_macros.h
index 1d9aff34..81931dc2 100644
--- a/src/core/include/mp-units/compat_macros.h
+++ b/src/core/include/mp-units/compat_macros.h
@@ -83,18 +83,6 @@
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 
-// IWYU pragma: begin_exports
-#if MP_UNITS_USE_FMTLIB
-MP_UNITS_DIAGNOSTIC_PUSH
-MP_UNITS_DIAGNOSTIC_IGNORE_UNREACHABLE
-MP_UNITS_DIAGNOSTIC_IGNORE_SHADOW
-#include <fmt/format.h>
-MP_UNITS_DIAGNOSTIC_POP
-#else
-#include <format>
-#endif
-// IWYU pragma: end_exports
-
 #endif
 
 #endif  // MP_UNITS_HOSTED
diff --git a/src/core/include/mp-units/ext/format.h b/src/core/include/mp-units/ext/format.h
new file mode 100644
index 00000000..72aca3a9
--- /dev/null
+++ b/src/core/include/mp-units/ext/format.h
@@ -0,0 +1,42 @@
+// 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
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+
+#include <mp-units/bits/requires_hosted.h>
+//
+#include <mp-units/bits/hacks.h>
+#include <mp-units/compat_macros.h>
+
+#if MP_UNITS_USE_FMTLIB
+MP_UNITS_DIAGNOSTIC_PUSH
+MP_UNITS_DIAGNOSTIC_IGNORE_UNREACHABLE
+MP_UNITS_DIAGNOSTIC_IGNORE_SHADOW
+#include <fmt/format.h>
+MP_UNITS_DIAGNOSTIC_POP
+#else
+#include <format>
+#endif
+
+#endif
diff --git a/test/runtime/almost_equals.h b/test/runtime/almost_equals.h
index 373e7943..0cc03e8e 100644
--- a/test/runtime/almost_equals.h
+++ b/test/runtime/almost_equals.h
@@ -22,6 +22,7 @@
 
 #include <catch2/matchers/catch_matchers_templated.hpp>
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <algorithm>
 #ifdef MP_UNITS_MODULES
 import mp_units;
diff --git a/test/runtime/fixed_string_test.cpp b/test/runtime/fixed_string_test.cpp
index 7efae3df..621118cb 100644
--- a/test/runtime/fixed_string_test.cpp
+++ b/test/runtime/fixed_string_test.cpp
@@ -25,6 +25,7 @@
 #include <mp-units/compat_macros.h>
 #include <sstream>
 #include <string_view>
+#include <mp-units/ext/format.h>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
diff --git a/test/runtime/fmt_test.cpp b/test/runtime/fmt_test.cpp
index 8c26ee28..b776edce 100644
--- a/test/runtime/fmt_test.cpp
+++ b/test/runtime/fmt_test.cpp
@@ -24,6 +24,7 @@
 #include <catch2/matchers/catch_matchers.hpp>
 #include <catch2/matchers/catch_matchers_exception.hpp>
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/format.h>
 #include <cstdint>
 #include <iomanip>
 #include <limits>
diff --git a/test/runtime/linear_algebra_test.cpp b/test/runtime/linear_algebra_test.cpp
index 4afb70d1..e55815fd 100644
--- a/test/runtime/linear_algebra_test.cpp
+++ b/test/runtime/linear_algebra_test.cpp
@@ -24,6 +24,7 @@
 #include <mp-units/compat_macros.h>
 #include <matrix>
 #include <ostream>
+#include <mp-units/ext/format.h>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
diff --git a/test/runtime/truncation_test.cpp b/test/runtime/truncation_test.cpp
index 6b05b767..af780d80 100644
--- a/test/runtime/truncation_test.cpp
+++ b/test/runtime/truncation_test.cpp
@@ -24,6 +24,7 @@
 #include <catch2/catch_template_test_macros.hpp>
 #include <catch2/catch_test_macros.hpp>
 #include <catch2/matchers/catch_matchers.hpp>
+#include <mp-units/ext/format.h>
 #include <limits>
 #include <numbers>
 #ifdef MP_UNITS_MODULES