diff --git a/src/yaku.erl b/src/yaku.erl
index d7fd17a..aefd827 100644
--- a/src/yaku.erl
+++ b/src/yaku.erl
@@ -9,12 +9,13 @@
 -include("../include/riichi.hrl").
 
 -export([yakuhai/2,
-        tanyao/2,
-        pinfu/2,
-        chiitoitsu/2,
-        kokushi_musou/2,
-        ryuu_iisou/2,
-        dai_san_gen/2]).
+         tanyao/2,
+         pinfu/2,
+         iipeikou/2,
+         chiitoitsu/2,
+         kokushi_musou/2,
+         ryuu_iisou/2,
+         dai_san_gen/2]).
 
 %% @doc Counts the pons/kans of value tiles in a player's hand.
 %%      Value tiles include all of the dragons, plus the round wind and the player's seat wind.
@@ -67,6 +68,25 @@ pinfu(#game{round=Round}, #player{seat=Seat, hand=Hand=#hand{melds=Melds}, drawn
         andalso HeadTile#tile.suit =/= dragon,
     Closed and OpenWait and Chiis and NonValuePair.
 
+%% @doc Counts unique elements in a list
+-spec count_unique(list()) -> list({term(), integer()}).
+count_unique(L) ->
+    Unique = sets:to_list(sets:from_list(L)),
+    [{I, length(lists:filter(fun (X) ->
+                                     X == I
+                             end,
+                             L))}
+     || I <- Unique].
+
+%% @doc Returns true for a hand containing two identical straights in the same suit
+%%      Will NOT return true if there are more than two, as this yaku and ryanpeikou
+%%      are mutually exclusive.
+-spec iipeikou(game(), player()) -> boolean().
+iipeikou(#game{}, #player{hand=#hand{melds=Melds}}) ->
+    Chiis = [M || M = #meld{type=chii} <- Melds],
+    Counts = [C || {_, C} <- count_unique(Chiis)],
+    lists:max(Counts) > 1 andalso lists:max(Counts) < 4.
+
 %% @doc Returns true for a 7-pair hand.
 -spec chiitoitsu(game(), player()) -> boolean().
 chiitoitsu(#game{}, #player{hand=#hand{tiles=[], melds=Melds}})
diff --git a/test/riichi_yaku_tests.erl b/test/riichi_yaku_tests.erl
index 78ed9b1..d7d6cd0 100644
--- a/test/riichi_yaku_tests.erl
+++ b/test/riichi_yaku_tests.erl
@@ -36,6 +36,14 @@ pinfu_test() ->
                         #meld{type=chii, tiles=[#tile{suit=man, value=V} || V <- [6,7,8]]}]},
     ?assertEqual(true, yaku:pinfu(#game{}, #player{hand=Hand, drawn={tsumo, #tile{suit=sou, value=6}}})).
 
+iipeikou_test() ->
+    Hand = #hand{melds=[#meld{type=pair, tiles=lists:duplicate(2, #tile{suit=sou, value=8})},
+                        #meld{type=chii, tiles=[#tile{suit=pin, value=V} || V <- [1,2,3]]},
+                        #meld{type=chii, tiles=[#tile{suit=sou, value=V} || V <- [4,5,6]]},
+                        #meld{type=chii, tiles=[#tile{suit=sou, value=V} || V <- [4,5,6]]},
+                        #meld{type=chii, tiles=[#tile{suit=man, value=V} || V <- [6,7,8]]}]},
+    ?assertEqual(true, yaku:iipeikou(#game{}, #player{hand=Hand, drawn={tsumo, #tile{suit=sou, value=6}}})).
+
 chiitoitsu_test() ->
     Hand = #hand{melds=[#meld{type=pair, tiles=lists:duplicate(2, #tile{suit=pin, value=V})} || V <- lists:seq(1,7)]},
     ?assertEqual(true, yaku:chiitoitsu(#game{}, #player{hand=Hand})).