diff --git a/Libplanet.Action/FeeCollector.cs b/Libplanet.Action/FeeCollector.cs
index bd1ce2971f9..ac693db8578 100644
--- a/Libplanet.Action/FeeCollector.cs
+++ b/Libplanet.Action/FeeCollector.cs
@@ -70,7 +70,7 @@ public IWorld Mortgage(IWorld world)
                 return world;
             }
 
-            IAccount account = world.GetFungibleAssetsAccount();
+            IAccount account = world.GetAccount(_context.SystemAccounts.FeeAccount);
             var balance = account.GetBalance(_context.Signer, realGasPrice.Currency);
             if (balance < realGasPrice * _context.GasLimit())
             {
@@ -86,7 +86,7 @@ public IWorld Mortgage(IWorld world)
                 _context.Signer,
                 realGasPrice * _context.GasLimit());
             _state = FeeCollectState.Mortgage;
-            return world.SetFungibleAssetsAccount(nextAccount);
+            return world.SetAccount(_context.SystemAccounts.FeeAccount, nextAccount);
         }
 
         public IWorld Refund(IWorld world)
@@ -108,12 +108,12 @@ public IWorld Refund(IWorld world)
                 return world;
             }
 
-            IAccount nextAccount = world.GetFungibleAssetsAccount().MintAsset(
+            IAccount nextAccount = world.GetAccount(_context.SystemAccounts.FeeAccount).MintAsset(
                 _context,
                 _context.Signer,
                 (_context.GasLimit() - _context.GasUsed()) * realGasPrice);
             _state = FeeCollectState.Refund;
-            return world.SetFungibleAssetsAccount(nextAccount);
+            return world.SetAccount(_context.SystemAccounts.FeeAccount, nextAccount);
         }
 
         public IWorld Reward(IWorld world)
@@ -135,12 +135,12 @@ public IWorld Reward(IWorld world)
                 return world;
             }
 
-            IAccount nextAccount = world.GetFungibleAssetsAccount().MintAsset(
+            IAccount nextAccount = world.GetAccount(_context.SystemAccounts.FeeAccount).MintAsset(
                 _context,
                 _context.Miner,
                 realGasPrice * _context.GasUsed());
             _state = FeeCollectState.Reward;
-            return world.SetFungibleAssetsAccount(nextAccount);
+            return world.SetAccount(_context.SystemAccounts.FeeAccount, nextAccount);
         }
 
         public IFeeCollector Next(IActionContext context)
diff --git a/Libplanet.Action/State/WorldExtensions.cs b/Libplanet.Action/State/WorldExtensions.cs
deleted file mode 100644
index e63d4de27b8..00000000000
--- a/Libplanet.Action/State/WorldExtensions.cs
+++ /dev/null
@@ -1,20 +0,0 @@
-using System.Collections.Immutable;
-using Bencodex.Types;
-using Libplanet.Crypto;
-
-namespace Libplanet.Action.State
-{
-    internal static class WorldExtensions
-    {
-        internal static IAccount GetFungibleAssetsAccount(this IWorldState world) =>
-            world.GetAccount(ReservedAddresses.DefaultAccount);
-
-        internal static IAccount GetValidatorSetAccount(this IWorldState world) =>
-            world.GetAccount(ReservedAddresses.DefaultAccount);
-
-        internal static IWorld SetFungibleAssetsAccount(
-            this IWorld world,
-            IAccount account) =>
-            world.SetAccount(ReservedAddresses.DefaultAccount, account);
-    }
-}