diff --git a/Framework/Units/PhysicalUnits.h b/Framework/Units/PhysicalUnits.h
index 23dbbb871dc7d5b2cd2d8538c2bbe7c6197c6812..5e7368dc6e62f0ce14c190e4f62144e3f4305b82 100644
--- a/Framework/Units/PhysicalUnits.h
+++ b/Framework/Units/PhysicalUnits.h
@@ -37,6 +37,7 @@ namespace corsika::units::si {
       phys::units::quantity<phys::units::electric_charge_d, double>;
   using EnergyType = phys::units::quantity<phys::units::energy_d, double>;
   using MassType = phys::units::quantity<phys::units::mass_d, double>;
+  using MassDensityType = phys::units::quantity<phys::units::mass_density_d, double>;
 
 } // end namespace corsika::units::si