diff --git a/include/xo/unit/quantity.hpp b/include/xo/unit/quantity.hpp
index 364ab216..70673ad9 100644
--- a/include/xo/unit/quantity.hpp
+++ b/include/xo/unit/quantity.hpp
@@ -158,7 +158,7 @@ namespace xo {
             Repr scale_ = Repr{};
         };
 
-        template < natural_unit<std::int64_t> NaturalUnit = natural_unit<std::int64_t>(),
+        template < natural_unit<std::int64_t> NaturalUnit,
                    typename Repr = double >
         using stdquantity = quantity<NaturalUnit, Repr>;