diff --git a/test/functional/feature_nulldummy.py b/test/functional/feature_nulldummy.py
--- a/test/functional/feature_nulldummy.py
+++ b/test/functional/feature_nulldummy.py
@@ -5,10 +5,9 @@
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
-from test_framework.mininode import CTransaction, network_thread_start
+from test_framework.mininode import CTransaction, FromHex, network_thread_start
 from test_framework.blocktools import create_coinbase, create_block
 from test_framework.script import CScript
-from io import BytesIO
 import time
 
 NULLDUMMY_ERROR = "64: non-mandatory-script-verify-flag (Dummy CHECKMULTISIG argument must be zero)"
@@ -90,9 +89,7 @@
         outputs = {to_address: amount}
         rawtx = node.createrawtransaction(inputs, outputs)
         signresult = node.signrawtransaction(rawtx)
-        tx = CTransaction()
-        f = BytesIO(hex_str_to_bytes(signresult['hex']))
-        tx.deserialize(f)
+        tx = FromHex(CTransaction(), signresult['hex'])
         return tx
 
     def block_submit(self, node, txs, accept=False):