diff --git a/src/systems/isq/include/mp-units/systems/isq/electromagnetism.h b/src/systems/isq/include/mp-units/systems/isq/electromagnetism.h
index de21ebc8..03294a36 100644
--- a/src/systems/isq/include/mp-units/systems/isq/electromagnetism.h
+++ b/src/systems/isq/include/mp-units/systems/isq/electromagnetism.h
@@ -60,9 +60,10 @@ QUANTITY_SPEC(magnetic_constant,
               electric_potential* time / (electric_current * length));  // TODO what is a correct equation here?
 inline constexpr auto permeability_of_vacuum = magnetic_constant;
 QUANTITY_SPEC(phase_speed_of_electromagnetic_waves, angular_frequency / angular_wavenumber);
-QUANTITY_SPEC(speed_of_light, speed);
-inline constexpr auto light_speed = speed_of_light;
-QUANTITY_SPEC(electric_constant, 1 / (magnetic_constant * pow<2>(speed_of_light)));
+QUANTITY_SPEC(speed_of_light_in_vacuum, speed);
+inline constexpr auto light_speed_in_vacuum = speed_of_light_in_vacuum;
+inline constexpr auto luminal_speed = speed_of_light_in_vacuum;
+QUANTITY_SPEC(electric_constant, 1 / (magnetic_constant * pow<2>(speed_of_light_in_vacuum)));
 inline constexpr auto permittivity_of_vacuum = electric_constant;
 QUANTITY_SPEC(permittivity, electric_flux_density / electric_field_strength, quantity_character::scalar);
 QUANTITY_SPEC(relative_permittivity, dimensionless, permittivity / electric_constant);
diff --git a/test/unit_test/static/isq_test.cpp b/test/unit_test/static/isq_test.cpp
index 151e5ad7..f61878de 100644
--- a/test/unit_test/static/isq_test.cpp
+++ b/test/unit_test/static/isq_test.cpp
@@ -280,8 +280,8 @@ static_assert(verify(isq::electromagnetic_energy_density, scalar, J / m3));
 static_assert(verify(isq::volumic_electromagnetic_energy, scalar, J / m3));
 static_assert(verify(isq::Poynting_vector, vector, W / m2));
 static_assert(verify(isq::phase_speed_of_electromagnetic_waves, scalar, m / s));
-static_assert(verify(isq::speed_of_light, scalar, m / s));
-static_assert(verify(isq::light_speed, scalar, m / s));
+static_assert(verify(isq::speed_of_light_in_vacuum, scalar, m / s));
+static_assert(verify(isq::light_speed_in_vacuum, scalar, m / s));
 static_assert(verify(isq::source_voltage, scalar, V));
 static_assert(verify(isq::source_tension, scalar, V));
 static_assert(verify(isq::scalar_magnetic_potential, scalar, A));