diff --git a/example/si_constants.cpp b/example/si_constants.cpp
index b7e8e009..f703fd71 100644
--- a/example/si_constants.cpp
+++ b/example/si_constants.cpp
@@ -38,13 +38,13 @@ int main()
                                1. * si2019::speed_of_light_in_vacuum, (1. * si2019::speed_of_light_in_vacuum)[m / s]);
   std::cout << STD_FMT::format("- Planck constant:                      {} = {:%.8eQ %q}\n",
                                1. * si2019::planck_constant, (1. * si2019::planck_constant)[J * s]);
-  // TODO uncomment the below when ISQ is done
-  // std::cout << STD_FMT::format("- elementary charge:                    {} = {:%.9eQ %q}\n",
-  //                              1. * si2019::elementary_charge, (1. * si2019::elementary_charge)[C]);
-  // std::cout << STD_FMT::format("- Boltzmann constant:                   {} = {:%.6eQ %q}\n",
-  //                              1. * si2019::boltzmann_constant, (1. * si2019::boltzmann_constant)[J / K]);
+  std::cout << STD_FMT::format("- elementary charge:                    {} = {:%.9eQ %q}\n",
+                               1. * si2019::elementary_charge, (1. * si2019::elementary_charge)[C]);
+  std::cout << STD_FMT::format("- Boltzmann constant:                   {} = {:%.6eQ %q}\n",
+                               1. * si2019::boltzmann_constant, (1. * si2019::boltzmann_constant)[J / K]);
   std::cout << STD_FMT::format("- Avogadro constant:                    {} = {:%.8eQ %q}\n",
                                1. * si2019::avogadro_constant, (1. * si2019::avogadro_constant)[1 / mol]);
+  // TODO uncomment the below when ISQ is done
   // std::cout << STD_FMT::format("- luminous efficacy:                    {} = {}\n", 1. * si2019::luminous_efficacy,
   //                              (1. * si2019::luminous_efficacy)[lm / W]);
 }
diff --git a/src/systems/si/include/units/si/constants.h b/src/systems/si/include/units/si/constants.h
index dfbb06f0..0239f46c 100644
--- a/src/systems/si/include/units/si/constants.h
+++ b/src/systems/si/include/units/si/constants.h
@@ -22,9 +22,7 @@
 
 #pragma once
 
-#include <units/isq/mechanics.h>
-#include <units/isq/space_and_time.h>
-#include <units/isq/thermodynamics.h>
+#include <units/isq/isq.h>
 #include <units/quantity.h>
 #include <units/si/units.h>
 
@@ -51,12 +49,12 @@ inline constexpr struct luminous_efficacy_unit :
 
 inline constexpr auto hyperfine_structure_transition_frequency_of_cs =
   isq::frequency[hyperfine_structure_transition_frequency_of_cs_unit];
-inline constexpr auto speed_of_light_in_vacuum = isq::speed[speed_of_light_in_vacuum_unit];
+inline constexpr auto speed_of_light_in_vacuum = isq::speed_of_light[speed_of_light_in_vacuum_unit];
 inline constexpr auto planck_constant = isq::action[planck_constant_unit];
-// TODO uncomment the below when all the ISQ is provided
-// inline constexpr auto elementary_charge = isq::electric_charge[elementary_charge_unit];
-// inline constexpr auto boltzmann_constant = isq::heat_capacity[boltzmann_constant_unit];
+inline constexpr auto elementary_charge = isq::electric_charge[elementary_charge_unit];
+inline constexpr auto boltzmann_constant = isq::entropy[boltzmann_constant_unit];
 inline constexpr auto avogadro_constant = (1 / isq::amount_of_substance)[avogadro_constant_unit];
+// TODO uncomment the below when all the ISQ is provided
 // inline constexpr auto luminous_efficacy = isq::luminous_efficacy_of_radiation[luminous_efficacy_unit];
 
 }  // namespace si2019