diff --git a/app.go b/app.go
index 6b21ef8cfa7..48c25ecbb33 100644
--- a/app.go
+++ b/app.go
@@ -331,7 +331,7 @@ func NewSimApp(
 	)
 
 	app.mm.RegisterInvariants(&app.CrisisKeeper)
-	app.mm.RegisterRoutes(app.Router(), app.QueryRouter(), codec.NewAminoCodec(encodingConfig.Amino))
+	app.mm.RegisterRoutes(app.Router(), app.QueryRouter(), encodingConfig.Amino)
 	app.mm.RegisterQueryServices(app.GRPCQueryRouter())
 
 	// add test gRPC service for testing gRPC queries in isolation
@@ -507,8 +507,6 @@ func (app *SimApp) SimulationManager() *module.SimulationManager {
 // API server.
 func (app *SimApp) RegisterAPIRoutes(apiSvr *api.Server) {
 	clientCtx := apiSvr.ClientCtx
-	// amino is needed here for backwards compatibility of REST routes
-	clientCtx = clientCtx.WithJSONMarshaler(clientCtx.LegacyAmino)
 	rpc.RegisterRoutes(clientCtx, apiSvr.Router)
 	authrest.RegisterTxRoutes(clientCtx, apiSvr.Router)
 	ModuleBasics.RegisterRESTRoutes(clientCtx, apiSvr.Router)
diff --git a/simd/cmd/genaccounts.go b/simd/cmd/genaccounts.go
index 67ffb88e20b..bda0fcba533 100644
--- a/simd/cmd/genaccounts.go
+++ b/simd/cmd/genaccounts.go
@@ -114,7 +114,7 @@ contain valid denominations. Accounts may optionally be supplied with vesting pa
 			}
 
 			genFile := config.GenesisFile()
-			appState, genDoc, err := genutiltypes.GenesisStateFromGenFile(depCdc, genFile)
+			appState, genDoc, err := genutiltypes.GenesisStateFromGenFile(genFile)
 			if err != nil {
 				return fmt.Errorf("failed to unmarshal genesis state: %w", err)
 			}
diff --git a/state.go b/state.go
index 54629441c3d..921aac5906c 100644
--- a/state.go
+++ b/state.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/tendermint/tendermint/crypto/secp256k1"
+	tmjson "github.com/tendermint/tendermint/libs/json"
 	tmtypes "github.com/tendermint/tendermint/types"
 
 	"github.com/cosmos/cosmos-sdk/codec"
@@ -56,7 +57,10 @@ func AppStateFn(cdc codec.JSONMarshaler, simManager *module.SimulationManager) s
 				panic(err)
 			}
 
-			cdc.MustUnmarshalJSON(bz, &appParams)
+			err = json.Unmarshal(bz, &appParams)
+			if err != nil {
+				panic(err)
+			}
 			appState, simAccs = AppStateRandomizedFn(simManager, r, cdc, accs, genesisTimestamp, appParams)
 
 		default:
@@ -132,10 +136,17 @@ func AppStateFromGenesisFileFn(r io.Reader, cdc codec.JSONMarshaler, genesisFile
 	}
 
 	var genesis tmtypes.GenesisDoc
-	cdc.MustUnmarshalJSON(bytes, &genesis)
+	// NOTE: Tendermint uses a custom JSON decoder for GenesisDoc
+	err = tmjson.Unmarshal(bytes, &genesis)
+	if err != nil {
+		panic(err)
+	}
 
 	var appState GenesisState
-	cdc.MustUnmarshalJSON(genesis.AppState, &appState)
+	err = json.Unmarshal(genesis.AppState, &appState)
+	if err != nil {
+		panic(err)
+	}
 
 	var authGenesis authtypes.GenesisState
 	if appState[authtypes.ModuleName] != nil {