diff --git a/src/types/auth.ts b/src/types/auth.ts
index e9eb8476..bb56e762 100644
--- a/src/types/auth.ts
+++ b/src/types/auth.ts
@@ -46,7 +46,13 @@ export interface DelayedVestingAccount extends AccountValue {
 }
 
 /** @TODO document */
-export interface StdTx extends TxValue {
+export interface StdTx {
+    type: string;
+    value: StdTxValue;
+}
+
+/** @TODO document */
+export interface StdTxValue extends TxValue {
     msg: Msg[];
     fee: StdFee;
     signatures: StdSignature[];
@@ -55,7 +61,7 @@ export interface StdTx extends TxValue {
 
 /** @TODO document */
 export interface StdFee {
-    amount: Coin[];
+    amount: Coin[] | null;
     gas: string;
 }
 
diff --git a/test/stdtx.test.ts b/test/stdtx.test.ts
new file mode 100644
index 00000000..199e05b8
--- /dev/null
+++ b/test/stdtx.test.ts
@@ -0,0 +1,67 @@
+import './setup';
+import { base64ToBytes, bytesToBase64 } from '@tendermint/belt';
+import * as Amino from '../';
+
+const txData = '2gEoKBapCkOoo2GaChTNi4afLkGQV1Df+AvNv4mvem6PjBIU0kxbneuQG/5QEXWWJm+hoPWFufEaEQoFc3Rha2USCDEwMDAwMDAwEhEKCwoFc3Rha2USAjQwEOa4AhpqCibrWumHIQL9AVlxawWaJcrGJl/aLlLAVxGHlI/BLzj3GC8Zi1a8wRJAummHUrkNaAcMCTg5K7E2SYgLoJA3Rh6MxpxvIcp9LQJ0NPhTCZ1WwuiKhwnKg3R/EU46/GQv7ktmTlPSDjrnCyIQKFNlbnQgdmlhIEx1bmllKQ==';
+
+const tx = {
+    'type':  'cosmos-sdk/StdTx',
+    'value': {
+        'msg':        [
+            {
+                'type':  'cosmos-sdk/MsgSend',
+                'value': {
+                    'from_address': 'cosmos1ek9cd8ewgxg9w5xllq9um0uf4aaxaruvcw4v9e',
+                    'to_address':   'cosmos16fx9h80tjqdlu5q3wktzvmap5r6ctw03myypaq',
+                    'amount':       [
+                        {
+                            'denom':  'stake',
+                            'amount': '10000000'
+                        }
+                    ]
+                }
+            }
+        ],
+        'fee':        {
+            'amount': [
+                {
+                    'denom':  'stake',
+                    'amount': '40'
+                }
+            ],
+            'gas':    '40038'
+        },
+        'signatures': [
+            {
+                'pub_key':   {
+                    'type':  'tendermint/PubKeySecp256k1',
+                    'value': 'Av0BWXFrBZolysYmX9ouUsBXEYeUj8EvOPcYLxmLVrzB'
+                },
+                'signature': 'ummHUrkNaAcMCTg5K7E2SYgLoJA3Rh6MxpxvIcp9LQJ0NPhTCZ1WwuiKhwnKg3R/EU46/GQv7ktmTlPSDjrnCw=='
+            }
+        ],
+        'memo':       '(Sent via Lunie)'
+    }
+};
+
+describe('StdTx', () => {
+    describe('decoding', () => {
+        describe('StdTx', () => {
+            it('decodes bytes', () => {
+                const bytes = base64ToBytes(txData);
+                const value = Amino.unmarshalStdTx(bytes, true);
+                expect(value).toMatchObject(tx);
+            });
+        });
+    });
+
+    describe('encoding', () => {
+        describe('StdTx', () => {
+            it('encodes value', () => {
+                const bytes = Amino.marshalStdTx(tx, true);
+                const data  = bytesToBase64(bytes);
+                expect(data).toBe(txData);
+            });
+        });
+    });
+});