diff --git a/.Lib9c.Tests/Model/State/CollectionStateTest.cs b/.Lib9c.Tests/Model/State/CollectionStateTest.cs
index b02dc0cf4b..bdd8d6d862 100644
--- a/.Lib9c.Tests/Model/State/CollectionStateTest.cs
+++ b/.Lib9c.Tests/Model/State/CollectionStateTest.cs
@@ -18,6 +18,8 @@ public void Bencoded()
                 {
                     1,
                     2,
+                    1,
+                    2,
                 },
             };
 
@@ -27,7 +29,7 @@ public void Bencoded()
             Assert.Equal(expected, serialized);
 
             var deserialized = new CollectionState(serialized);
-            Assert.Equal(state.Ids, deserialized.Ids);
+            Assert.Equal(new List<int> { 1, 2, }, deserialized.Ids);
         }
     }
 }
diff --git a/Lib9c/Model/State/CollectionState.cs b/Lib9c/Model/State/CollectionState.cs
index d77581e5da..6966218390 100644
--- a/Lib9c/Model/State/CollectionState.cs
+++ b/Lib9c/Model/State/CollectionState.cs
@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Linq;
 using Bencodex;
 using Bencodex.Types;
 using Nekoyume.Model.Stat;
@@ -24,13 +25,15 @@ public CollectionState(List serialized)
             {
                 Ids.Add((Integer)value);
             }
+
+            Ids = Ids.Distinct().ToList();
         }
 
         public CollectionState(IValue bencoded) : this((List)bencoded)
         {
         }
 
-        public IValue Bencoded => List.Empty.Add(new List(Ids));
+        public IValue Bencoded => List.Empty.Add(new List(Ids.Distinct()));
 
         public List<StatModifier> GetModifiers(CollectionSheet collectionSheet)
         {