diff --git a/include/xo/unit/basis_unit.hpp b/include/xo/unit/basis_unit.hpp
index 922470a0..94bdc949 100644
--- a/include/xo/unit/basis_unit.hpp
+++ b/include/xo/unit/basis_unit.hpp
@@ -64,6 +64,7 @@ namespace xo {
             constexpr basis_unit tonne            = basis_unit(dim::mass, scalefactor_ratio_type(      1000000,             1));
             constexpr basis_unit kilotonne        = basis_unit(dim::mass, scalefactor_ratio_type(   1000000000,             1));
             constexpr basis_unit megatonne        = basis_unit(dim::mass, scalefactor_ratio_type(1000000000000,             1));
+            constexpr basis_unit gigatonne        = basis_unit(dim::mass, scalefactor_ratio_type(1000000000000000,             1));
 
             // ----- distance -----
 
diff --git a/include/xo/unit/basis_unit_abbrev.hpp b/include/xo/unit/basis_unit_abbrev.hpp
index 49216d17..f6e1dfd2 100644
--- a/include/xo/unit/basis_unit_abbrev.hpp
+++ b/include/xo/unit/basis_unit_abbrev.hpp
@@ -60,6 +60,8 @@ namespace xo {
                         return basis_unit2_abbrev_type::from_chars("kt");
                     case 1000000000000:
                         return basis_unit2_abbrev_type::from_chars("Mt");
+                    case 1000000000000000:
+                        return basis_unit2_abbrev_type::from_chars("Gt");
                     }
                 }
 
diff --git a/include/xo/unit/natural_unit.hpp b/include/xo/unit/natural_unit.hpp
index bbd2f249..7617aade 100644
--- a/include/xo/unit/natural_unit.hpp
+++ b/include/xo/unit/natural_unit.hpp
@@ -368,6 +368,7 @@ namespace xo {
             constexpr auto tonne = natural_unit<std::int64_t>::from_bu(bu::tonne);
             constexpr auto kilotonne = natural_unit<std::int64_t>::from_bu(bu::kilotonne);
             constexpr auto megatonne = natural_unit<std::int64_t>::from_bu(bu::megatonne);
+            constexpr auto gigatonne = natural_unit<std::int64_t>::from_bu(bu::gigatonne);
 
             constexpr auto picometer = natural_unit<std::int64_t>::from_bu(bu::picometer);
             constexpr auto nanometer = natural_unit<std::int64_t>::from_bu(bu::nanometer);