diff --git a/ray.cpp b/ray.cpp
index dcc3cb71..23218c35 100644
--- a/ray.cpp
+++ b/ray.cpp
@@ -121,6 +121,18 @@ ray<S,T>::at (T t) const
 }
 
 
+///////////////////////////////////////////////////////////////////////////////
+template <size_t S, typename T>
+std::ostream&
+util::operator<< (std::ostream &os, ray<S,T> r)
+{
+    return os << "ray(" << r.origin << ',' << r.direction << ')';
+}
+
+template std::ostream& util::operator<< (std::ostream&, ray<3,float>);
+template std::ostream& util::operator<< (std::ostream&, ray<3,double>);
+
+
 ///////////////////////////////////////////////////////////////////////////////
 template struct util::ray<2,float>;
 template struct util::ray<3,float>;
diff --git a/ray.hpp b/ray.hpp
index 4e4af2ff..ac95cabf 100644
--- a/ray.hpp
+++ b/ray.hpp
@@ -24,6 +24,8 @@
 #include "sphere.hpp"
 #include "vector.hpp"
 
+#include <iostream>
+
 namespace util {
     template <size_t S, typename T>
     struct ray {
@@ -45,6 +47,8 @@ namespace util {
         vector<S,T> direction;
     };
 
+    template <size_t S, typename T>
+    std::ostream& operator<< (std::ostream&, ray<S,T>);
 
     typedef ray<2,float> ray2f;
     typedef ray<3,float> ray3f;