diff --git a/include/boost/ratio/ratio.hpp b/include/boost/ratio/ratio.hpp
index 6278291..e670763 100644
--- a/include/boost/ratio/ratio.hpp
+++ b/include/boost/ratio/ratio.hpp
@@ -38,11 +38,11 @@ time2_demo contained this comment:
 namespace boost
 {
 
-template <class R1, class R2> struct ratio_gcd: ratio<
+// extension used by Chrono
+
+template <class R1, class R2> using ratio_gcd = typename ratio<
     ratio_detail::gcd<R1::num, R2::num>::value,
-    ratio_detail::lcm<R1::den, R2::den>::value>::type
-{
-};
+    ratio_detail::lcm<R1::den, R2::den>::value>::type;
 
 }  // namespace boost
 
diff --git a/include/boost/ratio/ratio_fwd.hpp b/include/boost/ratio/ratio_fwd.hpp
index 6dc71ad..a044c9b 100644
--- a/include/boost/ratio/ratio_fwd.hpp
+++ b/include/boost/ratio/ratio_fwd.hpp
@@ -52,10 +52,6 @@ using std::ratio_subtract;
 using std::ratio_multiply;
 using std::ratio_divide;
 
-// extension used by Chrono
-template <class R1, class R2> struct ratio_gcd;
-// template <class R1, class R2> struct ratio_lcm;
-
 // ratio comparison
 using std::ratio_equal;
 using std::ratio_not_equal;