diff --git a/src/core/include/mp-units/bits/constexpr_math.h b/src/core/include/mp-units/bits/constexpr_math.h
index fd88b9e5..8dc66aa5 100644
--- a/src/core/include/mp-units/bits/constexpr_math.h
+++ b/src/core/include/mp-units/bits/constexpr_math.h
@@ -39,6 +39,12 @@ import std;
 
 namespace mp_units::detail {
 
+template<typename T>
+[[nodiscard]] MP_UNITS_CONSTEVAL T abs(T v) noexcept
+{
+  return v < 0 ? -v : v;
+}
+
 // Raise an arbitrary arithmetic type to a positive integer power at compile time.
 template<typename T>
 [[nodiscard]] consteval T int_power(T base, std::integral auto exp)
diff --git a/src/core/include/mp-units/bits/ratio.h b/src/core/include/mp-units/bits/ratio.h
index 329f5106..4a06147c 100644
--- a/src/core/include/mp-units/bits/ratio.h
+++ b/src/core/include/mp-units/bits/ratio.h
@@ -22,6 +22,7 @@
 
 #pragma once
 
+#include <mp-units/bits/constexpr_math.h>
 #include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
 #include <mp-units/compat_macros.h>
@@ -39,12 +40,6 @@ import std;
 
 namespace mp_units::detail {
 
-template<typename T>
-[[nodiscard]] MP_UNITS_CONSTEVAL T abs(T v) noexcept
-{
-  return v < 0 ? -v : v;
-}
-
 [[nodiscard]] consteval std::intmax_t safe_multiply(std::intmax_t lhs, std::intmax_t rhs)
 {
   constexpr std::intmax_t c = std::uintmax_t{1} << (sizeof(std::intmax_t) * 4);