diff --git a/test/vector.cpp b/test/vector.cpp
index ba4a82a5..e1134f5e 100644
--- a/test/vector.cpp
+++ b/test/vector.cpp
@@ -115,7 +115,7 @@ main ()
     tap.expect (!is_normalised (util::vector3f::ONES), "ones isn't normalised");
 
     tap.expect_eq (
-        util::hypot (util::vector3f{0,1,2}, util::vector3f{3,2,4}),
+        util::hypot (util::vector3f{0,1,2} - util::vector3f{3,2,4}),
         std::sqrt (14.f),
         "vector3f hypot"
     );
diff --git a/vector.hpp b/vector.hpp
index 523d1fc8..060b332a 100644
--- a/vector.hpp
+++ b/vector.hpp
@@ -50,11 +50,11 @@ namespace util {
     template <typename T> vector<2,T> to_euler   (vector<3,T>);
     template <typename T> vector<3,T> from_euler (vector<2,T>);
 
-    // power functions
+    // root of sum of squares
     template <size_t S, typename T>
     constexpr
     T
-    hypot (util::vector<S,T>, util::vector<S,T>);
+    hypot (util::vector<S,T>);
 
     // output and serialisation operators
     template <size_t S, typename T>
diff --git a/vector.ipp b/vector.ipp
index e9624569..11897cf8 100644
--- a/vector.ipp
+++ b/vector.ipp
@@ -38,8 +38,7 @@ util::vector<S,T>::homog (void) const
 template <size_t S, typename T>
 constexpr
 T
-util::hypot (util::vector<S,T> a, util::vector<S,T> b)
+util::hypot (util::vector<S,T> v)
 {
-    auto c  = a - b;
-    return std::sqrt (sum (c * c));
+    return std::sqrt (sum (v * v));
 }