diff --git a/bigchaindb/tendermint/lib.py b/bigchaindb/tendermint/lib.py
index 3cf93ce5..66b568e2 100644
--- a/bigchaindb/tendermint/lib.py
+++ b/bigchaindb/tendermint/lib.py
@@ -41,10 +41,9 @@ class BigchainDB(Bigchain):
         # TODO: handle connection errors!
         requests.post(ENDPOINT, json=payload)
 
-    def write_transaction(self, transaction, **kwargs):
+    def write_transaction(self, transaction, **mode):
         # This method offers backward compatibility with the Web API.
         """Submit a valid transaction to the mempool."""
-        mode = kwargs
         self.post_transaction(transaction, mode)
 
     def store_transaction(self, transaction):
diff --git a/bigchaindb/web/views/transactions.py b/bigchaindb/web/views/transactions.py
index e49cd189..e53058b4 100644
--- a/bigchaindb/web/views/transactions.py
+++ b/bigchaindb/web/views/transactions.py
@@ -56,10 +56,9 @@ class TransactionListApi(Resource):
             A ``dict`` containing the data about the transaction.
         """
         parser = reqparse.RequestParser()
-        parser.add_argument('mode', type=parameters.valid_mode)
+        parser.add_argument('mode', type=parameters.valid_mode,
+                            default='broadcast_tx_async')
         args = parser.parse_args()
-        if not str(args['mode']) or str(args['mode']) == 'None':
-            args['mode'] = 'broadcast_tx_async'
 
         pool = current_app.config['bigchain_pool']
 
diff --git a/tests/web/test_transactions.py b/tests/web/test_transactions.py
index 39e1a00b..a67d790e 100644
--- a/tests/web/test_transactions.py
+++ b/tests/web/test_transactions.py
@@ -446,3 +446,5 @@ def test_post_transaction_invalid_mode(client):
     mode_endpoint = TX_ENDPOINT + '?mode=nope'
     response = client.post(mode_endpoint, data=json.dumps(tx.to_dict()))
     assert '400 BAD REQUEST' in response.status
+    assert 'Mode must be "async", "sync" or "commit"' ==\
+           json.loads(response.data.decode('utf8'))['message']['mode']