diff --git a/src/include/units/current.h b/src/include/units/current.h
index e6738d9d..eb989fe3 100644
--- a/src/include/units/current.h
+++ b/src/include/units/current.h
@@ -36,7 +36,7 @@ namespace units {
   template<Unit U = struct ampere, Number Rep = double>
   using current = quantity<dimension_current, U, Rep>;
 
-  struct ampere : unit<dimension_current, std::ratio<1>> {};
+  struct ampere : unit<dimension_current> {};
   template<> struct upcasting_traits<upcast_from<ampere>> : upcast_to<ampere> {};
 
   inline namespace literals {
diff --git a/src/include/units/length.h b/src/include/units/length.h
index 880fca88..c9c90a2a 100644
--- a/src/include/units/length.h
+++ b/src/include/units/length.h
@@ -37,7 +37,7 @@ namespace units {
   using length = quantity<dimension_length, U, Rep>;
 
   // SI units
-  struct meter : unit<dimension_length, std::ratio<1>> {};
+  struct meter : unit<dimension_length> {};
   template<> struct upcasting_traits<upcast_from<meter>> : upcast_to<meter> {};
 
   struct millimeter : milli<meter> {};
diff --git a/src/include/units/luminous_intensity.h b/src/include/units/luminous_intensity.h
index 3838bb8b..3fe05d04 100644
--- a/src/include/units/luminous_intensity.h
+++ b/src/include/units/luminous_intensity.h
@@ -36,7 +36,7 @@ namespace units {
   template<Unit U = struct candela, Number Rep = double>
   using luminous_intensity = quantity<dimension_luminous_intensity, U, Rep>;
 
-  struct candela : unit<dimension_luminous_intensity, std::ratio<1>> {};
+  struct candela : unit<dimension_luminous_intensity> {};
   template<> struct upcasting_traits<upcast_from<candela>> : upcast_to<candela> {};
 
   inline namespace literals {
diff --git a/src/include/units/substance.h b/src/include/units/substance.h
index 0bc47c3c..4fe89d84 100644
--- a/src/include/units/substance.h
+++ b/src/include/units/substance.h
@@ -36,7 +36,7 @@ namespace units {
   template<Unit U = struct mole, Number Rep = double>
   using substance = quantity<dimension_substance, U, Rep>;
 
-  struct mole : unit<dimension_substance, std::ratio<1>> {};
+  struct mole : unit<dimension_substance> {};
   template<> struct upcasting_traits<upcast_from<mole>> : upcast_to<mole> {};
 
   inline namespace literals {
diff --git a/src/include/units/temperature.h b/src/include/units/temperature.h
index 6ee89357..9191ffd9 100644
--- a/src/include/units/temperature.h
+++ b/src/include/units/temperature.h
@@ -36,7 +36,7 @@ namespace units {
   template<Unit U = struct kelvin, Number Rep = double>
   using temperature = quantity<dimension_temperature, U, Rep>;
 
-  struct kelvin : unit<dimension_temperature, std::ratio<1>> {};
+  struct kelvin : unit<dimension_temperature> {};
   template<> struct upcasting_traits<upcast_from<kelvin>> : upcast_to<kelvin> {};
 
   inline namespace literals {
diff --git a/src/include/units/time.h b/src/include/units/time.h
index f695ca62..d1bec3d3 100644
--- a/src/include/units/time.h
+++ b/src/include/units/time.h
@@ -36,7 +36,7 @@ namespace units {
   template<Unit U = struct second, Number Rep = double>
   using time = quantity<dimension_time, U, Rep>;
 
-  struct second : unit<dimension_time, std::ratio<1>> {};
+  struct second : unit<dimension_time> {};
   template<> struct upcasting_traits<upcast_from<second>> : upcast_to<second> {};
 
   struct nanosecond : nano<second> {};
diff --git a/src/include/units/unit.h b/src/include/units/unit.h
index 3125f465..8ed2e954 100644
--- a/src/include/units/unit.h
+++ b/src/include/units/unit.h
@@ -27,7 +27,7 @@
 
 namespace units {
 
-  template<Dimension D, Ratio R>
+  template<Dimension D, Ratio R = std::ratio<1>>
     requires (R::num > 0)
   struct unit : upcast_base<unit<D, R>> {
     using dimension = D;