diff --git a/src/core/include/mp-units/bits/external/fixed_string.h b/src/core/include/mp-units/bits/external/fixed_string.h
index d7fb80f4..44844911 100644
--- a/src/core/include/mp-units/bits/external/fixed_string.h
+++ b/src/core/include/mp-units/bits/external/fixed_string.h
@@ -22,9 +22,9 @@
 
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>  // IWYU pragma: keep
 // TODO use <algorithm> when moved to C++20 modules (parsing takes too long for each translation unit)
 #include <mp-units/bits/external/algorithm.h>
+#include <mp-units/compat_macros.h>  // IWYU pragma: keep
 
 // IWYU pragma: begin_exports
 #include <compare>
diff --git a/src/core/include/mp-units/bits/external/hacks.h b/src/core/include/mp-units/bits/external/hacks.h
index a24a884a..e424d997 100644
--- a/src/core/include/mp-units/bits/external/hacks.h
+++ b/src/core/include/mp-units/bits/external/hacks.h
@@ -108,46 +108,3 @@
 #define MP_UNITS_CONSTRAINED_NTTP_WORKAROUND(X) X
 
 #endif
-
-#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
-
-#define MP_UNITS_STD_FMT fmt
-#define MP_UNITS_FMT_LOCALE(loc) (loc).template get<std::locale>()
-#define MP_UNITS_FMT_TO_ARG_ID(arg) (arg)
-#define MP_UNITS_FMT_FROM_ARG_ID(arg) (arg)
-
-// This re-uses code from fmt;
-#if FMT_EXCEPTIONS
-#if FMT_MSC_VERSION || defined(__NVCC__)
-#define MP_UNITS_THROW(x) ::fmt::detail::do_throw(x)
-#else
-#define MP_UNITS_THROW(x) throw x
-#endif
-#else
-#define MP_UNITS_THROW(x)          \
-  do {                             \
-    FMT_ASSERT(false, (x).what()); \
-  } while (false)
-#endif
-
-#else
-
-#if !defined __cpp_lib_format && !defined MP_UNITS_COMP_CLANG
-#error "std::formatting facility not supported"
-#endif
-
-#include <format>
-
-#define MP_UNITS_STD_FMT std
-#define MP_UNITS_FMT_LOCALE(loc) loc
-#define MP_UNITS_FMT_TO_ARG_ID(arg) static_cast<std::size_t>(arg)
-#define MP_UNITS_FMT_FROM_ARG_ID(arg) static_cast<int>(arg)
-#define MP_UNITS_THROW(arg) throw arg
-
-#endif
diff --git a/src/core/include/mp-units/compat_macros.h b/src/core/include/mp-units/compat_macros.h
index 4ab02761..25666a0d 100644
--- a/src/core/include/mp-units/compat_macros.h
+++ b/src/core/include/mp-units/compat_macros.h
@@ -37,3 +37,46 @@
   } name
 
 #endif
+
+#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
+
+#define MP_UNITS_STD_FMT fmt
+#define MP_UNITS_FMT_LOCALE(loc) (loc).template get<std::locale>()
+#define MP_UNITS_FMT_TO_ARG_ID(arg) (arg)
+#define MP_UNITS_FMT_FROM_ARG_ID(arg) (arg)
+
+// This re-uses code from fmt;
+#if FMT_EXCEPTIONS
+#if FMT_MSC_VERSION || defined(__NVCC__)
+#define MP_UNITS_THROW(x) ::fmt::detail::do_throw(x)
+#else
+#define MP_UNITS_THROW(x) throw x
+#endif
+#else
+#define MP_UNITS_THROW(x)          \
+  do {                             \
+    FMT_ASSERT(false, (x).what()); \
+  } while (false)
+#endif
+
+#else
+
+#if !defined __cpp_lib_format && !defined MP_UNITS_COMP_CLANG
+#error "std::formatting facility not supported"
+#endif
+
+#include <format>
+
+#define MP_UNITS_STD_FMT std
+#define MP_UNITS_FMT_LOCALE(loc) loc
+#define MP_UNITS_FMT_TO_ARG_ID(arg) static_cast<std::size_t>(arg)
+#define MP_UNITS_FMT_FROM_ARG_ID(arg) static_cast<int>(arg)
+#define MP_UNITS_THROW(arg) throw arg
+
+#endif