diff --git a/src/riichi.erl b/src/riichi.erl
index ca6a461..f9a54b0 100644
--- a/src/riichi.erl
+++ b/src/riichi.erl
@@ -103,6 +103,17 @@ score_hand(#hand{}=Hand, BaseFu, Limit) ->
                     _ -> 0
                 end
         end,
+        _Ryuu_Ii_Sou = fun(#hand{}=H) ->
+                Set = sets:from_list(H#hand.tiles),
+                Greens = sets:from_list(lists:flatten([
+                            [#tile{suit=sou, value=V} || V <- [2,3,4,6,8]],
+                            [#tile{suit=dragon, value=green}]
+                        ])),
+                case sets:is_subset(Set, Greens) of
+                    true -> 13;
+                    _ -> 0
+                end
+        end,
         _Kokushi_Musou = fun(#hand{}=H) ->
                 Sets = find_sets(H#hand.tiles),
                 Terminals = not lists:any(fun(#tile{value=V}) -> lists:member(V, lists:seq(2,8)) end, H#hand.tiles),
diff --git a/test/riichi_tests.erl b/test/riichi_tests.erl
index 03c11d0..54e42bc 100644
--- a/test/riichi_tests.erl
+++ b/test/riichi_tests.erl
@@ -115,3 +115,14 @@ score_hand_kokushi_musou_test() ->
             [#tile{suit=pin, value=1}]])
     },
     ?assertEqual(riichi:score_hand(Hand, 30), 8000).
+
+score_hand_ryuu_ii_sou_test() ->
+    Hand = #hand{
+        tiles = lists:flatten([
+            [#tile{suit=sou, value=V} || V <- [2,3,4]],
+            [#tile{suit=sou, value=V} || V <- [2,3,4]],
+            lists:duplicate(3, #tile{suit=sou, value=6}),
+            lists:duplicate(3, #tile{suit=sou, value=8}),
+            lists:duplicate(2, #tile{suit=dragon, value=green})])
+    },
+    ?assertEqual(riichi:score_hand(Hand, 30), 8000).