diff --git a/src/include/units/bits/stdconcepts.h b/src/include/units/bits/stdconcepts.h
index 5735dd24..9b73068e 100644
--- a/src/include/units/bits/stdconcepts.h
+++ b/src/include/units/bits/stdconcepts.h
@@ -29,14 +29,14 @@ namespace mp {
 
   namespace detail {
     template<class T, class U>
-    bool concept SameHelper = std::is_same_v<T, U>;
+    concept bool SameHelper = std::is_same_v<T, U>;
   }
 
   template<class T, class U>
-  bool concept Same = detail::SameHelper<T, U> && detail::SameHelper<U, T>;
+  concept bool Same = detail::SameHelper<T, U> && detail::SameHelper<U, T>;
 
   template <class From, class To>
-  bool concept ConvertibleTo = std::is_convertible_v<From, To> &&
+  concept bool ConvertibleTo = std::is_convertible_v<From, To> &&
       requires(From (&f)()) {
           static_cast<To>(f());
       };
diff --git a/src/include/units/bits/tools.h b/src/include/units/bits/tools.h
index 9e74ee32..713b7c4d 100644
--- a/src/include/units/bits/tools.h
+++ b/src/include/units/bits/tools.h
@@ -69,7 +69,7 @@ namespace mp {
   }
 
   template<typename T>
-  bool concept Ratio = detail::is_ratio<T>::value;
+  concept bool Ratio = detail::is_ratio<T>::value;
 
   // common_ratio
 
diff --git a/src/include/units/dimension.h b/src/include/units/dimension.h
index 35fa36f5..9524dc94 100644
--- a/src/include/units/dimension.h
+++ b/src/include/units/dimension.h
@@ -58,7 +58,7 @@ namespace units {
   }
 
   template<typename T>
-  bool concept Exponent = detail::is_exp<T>::value;
+  concept bool Exponent = detail::is_exp<T>::value;
 
 
   // exp_less
@@ -83,7 +83,7 @@ namespace units {
   // dimension
 
   template<Exponent... Es>
-  using dimension = mp::type_list<Es...>;
+  struct dimension;
 
   // is_dimension
   namespace detail {
@@ -95,7 +95,7 @@ namespace units {
   }
 
   template<typename T>
-  bool concept Dimension = detail::is_dimension<T>::value;
+  concept bool Dimension = detail::is_dimension<T>::value;
 
 
   // make_dimension
diff --git a/src/include/units/quantity.h b/src/include/units/quantity.h
index b821b95c..1821b2d3 100644
--- a/src/include/units/quantity.h
+++ b/src/include/units/quantity.h
@@ -46,7 +46,7 @@ namespace units {
   }
 
   template<typename T>
-  bool concept Quantity = detail::is_quantity<T>::value;
+  concept bool Quantity = detail::is_quantity<T>::value;
 
   // treat_as_floating_point