diff --git a/src/Hanafuda/KoiKoi/Game.hs b/src/Hanafuda/KoiKoi/Game.hs
index 379719d..50b7b00 100644
--- a/src/Hanafuda/KoiKoi/Game.hs
+++ b/src/Hanafuda/KoiKoi/Game.hs
@@ -25,7 +25,7 @@ import Control.Monad.IO.Class (MonadIO)
 import Control.Monad.Writer (MonadWriter)
 import Data.Map (Map)
 import Hanafuda (Card, Flower, Pack)
-import Hanafuda.ID (ID)
+import Hanafuda.ID (ID, IDType(..), Prefix(..))
 import qualified Hanafuda.KoiKoi.Yaku as KoiKoi (Score)
 import qualified Hanafuda.Player as Player (ID, Players, Player, Scores, set)
 
@@ -45,6 +45,8 @@ type PlayerID = Player.ID KoiKoi.Score
 type Players = Player.Players KoiKoi.Score
 type Scores = Player.Scores KoiKoi.Score
 type GameID = ID Game
+instance IDType Game where
+  prefix = Prefix "Game"
 type PlayerTurn = Map PlayerID PlayerID
 
 data Game = Game {