diff --git a/colour.hpp b/colour.hpp
index e2174b50..de23b08a 100644
--- a/colour.hpp
+++ b/colour.hpp
@@ -29,8 +29,8 @@
 namespace util {
     /// An RGBA colour POD type.
     template <typename T>
-    struct colour : public coord::base<4,T,coord::rgba> {
-        using coord::base<4,T,coord::rgba>::base;
+    struct colour : public coord::base<4,T,colour,coord::rgba> {
+        using coord::base<4,T,util::colour,coord::rgba>::base;
 
         static const colour WHITE;
         static const colour BLACK;
diff --git a/coord/base.hpp b/coord/base.hpp
index cbd09701..13bd1f93 100644
--- a/coord/base.hpp
+++ b/coord/base.hpp
@@ -27,7 +27,7 @@
 
 namespace util { namespace coord {
     /////////////////////////////////////////////////////////////////////////
-    template <size_t S, typename T, typename ...tags>
+    template <size_t S, typename T, template <size_t, typename> class KLASS, typename ...tags>
     struct base : public init <S,T,tags...> {
         static_assert (S > 0, "coord dimensions must be strictly positive");
 
@@ -44,8 +44,8 @@ namespace util { namespace coord {
         explicit base (T v)
         { std::fill (std::begin (this->data), std::end (this->data), v); }
 
-        base (const base<S,T,tags...> &rhs) = default;
-        base& operator= (const base<S,T,tags...> &rhs) = default;
+        base (const base<S,T,KLASS,tags...> &rhs) = default;
+        base& operator= (const base<S,T,KLASS,tags...> &rhs) = default;
 
         // element accessors
         T& operator[] (size_t i)       { return this->data[i]; }
@@ -57,6 +57,7 @@ namespace util { namespace coord {
         T* begin (void) { return std::begin (this->data); }
         T* end   (void) { return std::end   (this->data); }
 
+        ///////////////////////////////////////////////////////////////////////
         // conversions
         template <template <size_t, typename> class K>
         K<S,T> as (void) const
diff --git a/extent.hpp b/extent.hpp
index ce47b157..ef559b47 100644
--- a/extent.hpp
+++ b/extent.hpp
@@ -30,9 +30,9 @@ namespace util {
      * A pure two-dimensional size, without positioning
      */
     template <size_t S, typename T>
-    struct extent : public coord::base<S,T,coord::whd>
+    struct extent : public coord::base<S,T,extent,coord::whd>
     {
-        using coord::base<S,T,coord::whd>::base;
+        using coord::base<S,T,util::extent,coord::whd>::base;
 
         extent () = default;
         extent (vector<S,T>);
diff --git a/point.hpp b/point.hpp
index c54efcc7..dc674395 100644
--- a/point.hpp
+++ b/point.hpp
@@ -32,9 +32,9 @@
 namespace util {
     /// An n-dimensional position in space.
     template <size_t S, typename T>
-    struct point : public coord::base<S,T,coord::xyzw>
+    struct point : public coord::base<S,T,point,coord::xyzw>
     {
-        using coord::base<S,T,coord::xyzw>::base;
+        using coord::base<S,T,util::point,coord::xyzw>::base;
 
         // point operators
         template <typename U> typename std::common_type<T,U>::type distance  (const point<S,U> &) const;
diff --git a/vector.hpp b/vector.hpp
index e940b3b9..891583f8 100644
--- a/vector.hpp
+++ b/vector.hpp
@@ -29,8 +29,9 @@
 
 namespace util {
     template <size_t S, typename T>
-    struct vector : public coord::base<S,T,coord::xyzw,coord::stpq> {
-        using coord::base<S,T,coord::xyzw,coord::stpq>::base;
+    struct vector : public coord::base<S,T,vector,coord::xyzw,coord::stpq>
+    {
+        using coord::base<S,T,util::vector,coord::xyzw,coord::stpq>::base;
 
         bool is_zero (void) const;