diff --git a/src/core/include/mp-units/quantity.h b/src/core/include/mp-units/quantity.h
index 3d3642b3d..c85bc0bec 100644
--- a/src/core/include/mp-units/quantity.h
+++ b/src/core/include/mp-units/quantity.h
@@ -151,6 +151,7 @@ class quantity {
   quantity& operator=(quantity&&) = default;
 
   // data access
+  [[nodiscard]] constexpr rep& number() & noexcept { return number_; }
   [[nodiscard]] constexpr const rep& number() const& noexcept { return number_; }
   [[nodiscard]] constexpr rep&& number() && noexcept { return std::move(number_); }
   [[nodiscard]] constexpr const rep&& number() const&& noexcept { return std::move(number_); }