diff --git a/include/xo/unit/quantity.hpp b/include/xo/unit/quantity.hpp
index 0df8ec74..588c45ec 100644
--- a/include/xo/unit/quantity.hpp
+++ b/include/xo/unit/quantity.hpp
@@ -502,6 +502,7 @@ namespace xo {
              *  @pre @c Quantity2 must have the same dimension as @c *this.
              **/
             template <typename Quantity2>
+            requires quantity_concept<Quantity2> && same_dimension_v<unit_type, typename Quantity2::unit_type>
             constexpr operator Quantity2 () const {
                 /* avoid truncating precision when converting:
                  * use best available representation
diff --git a/include/xo/unit/ratio_util.hpp b/include/xo/unit/ratio_util.hpp
index 1d7e3199..970068d8 100644
--- a/include/xo/unit/ratio_util.hpp
+++ b/include/xo/unit/ratio_util.hpp
@@ -13,7 +13,7 @@ namespace xo {
 
         template <typename Ratio>
         struct ratio_floor {
-            using type = std::ratio<Ratio::num/Ratio::den>;
+            using type = std::ratio<Ratio::num/Ratio::den, 1>;
         };
 
         template <typename Ratio>