diff --git a/src/systems/include/mp-units/systems/isq/space_and_time.h b/src/systems/include/mp-units/systems/isq/space_and_time.h
index 2157a299..a123f6dd 100644
--- a/src/systems/include/mp-units/systems/isq/space_and_time.h
+++ b/src/systems/include/mp-units/systems/isq/space_and_time.h
@@ -66,10 +66,8 @@ inline constexpr auto wavenumber = repetency;
 QUANTITY_SPEC(wave_vector, repetency, quantity_character::vector);
 QUANTITY_SPEC(angular_repetency, inverse(wavelength));
 inline constexpr auto angular_wavenumber = angular_repetency;
-QUANTITY_SPEC(phase_velocity, angular_frequency / angular_repetency);
-inline constexpr auto phase_speed = phase_velocity;
-QUANTITY_SPEC(group_velocity, angular_frequency / angular_repetency);
-inline constexpr auto group_speed = group_velocity;
+QUANTITY_SPEC(phase_speed, angular_frequency / angular_repetency);
+QUANTITY_SPEC(group_speed, angular_frequency / angular_repetency);
 QUANTITY_SPEC(damping_coefficient, inverse(time_constant));
 QUANTITY_SPEC(logarithmic_decrement, dimensionless, damping_coefficient* period_duration);
 QUANTITY_SPEC(attenuation, inverse(distance));
diff --git a/test/static/isq_test.cpp b/test/static/isq_test.cpp
index c7dc8ffb..6e90cd11 100644
--- a/test/static/isq_test.cpp
+++ b/test/static/isq_test.cpp
@@ -79,9 +79,7 @@ static_assert(verify(isq::wavenumber, scalar, one / m));
 static_assert(verify(isq::wave_vector, vector, one / m));
 static_assert(verify(isq::angular_repetency, scalar, one / m));
 static_assert(verify(isq::angular_wavenumber, scalar, one / m));
-static_assert(verify(isq::phase_velocity, scalar, m / s));
 static_assert(verify(isq::phase_speed, scalar, m / s));
-static_assert(verify(isq::group_velocity, scalar, m / s));
 static_assert(verify(isq::group_speed, scalar, m / s));
 static_assert(verify(isq::damping_coefficient, scalar, one / s));
 static_assert(verify(isq::logarithmic_decrement, scalar, one));