diff --git a/src/systems/si/include/units/isq/si/constants.h b/src/systems/si/include/units/isq/si/constants.h
index 4b3928d0..79884577 100644
--- a/src/systems/si/include/units/isq/si/constants.h
+++ b/src/systems/si/include/units/isq/si/constants.h
@@ -52,7 +52,7 @@ template<Representation Rep = double>
 inline constexpr auto speed_of_light = speed<metre_per_second, Rep>(299'792'458);
 
 template<Representation Rep = double>
-inline constexpr auto hyperfine_structure_transition_frequency = frequency<hertz, Rep>(9'192'631'770);
+inline constexpr auto hyperfine_structure_transition_frequency = frequency<hertz, Rep>(Rep{9'192'631'770});
 
 template<Representation Rep = double>
 inline constexpr auto luminous_efficacy = luminous_flux<lumen, Rep>(683) / power<watt, Rep>(1);