diff --git a/test/functional/feature_nulldummy.py b/test/functional/feature_nulldummy.py
index 5ec262598..b4f29fd37 100755
--- a/test/functional/feature_nulldummy.py
+++ b/test/functional/feature_nulldummy.py
@@ -1,119 +1,117 @@
 #!/usr/bin/env python3
 # Copyright (c) 2016 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
-from test_framework.messages import FromHex
+from test_framework.messages import FromHex, ToHex
 from test_framework.mininode import CTransaction, network_thread_start
 from test_framework.blocktools import create_coinbase, create_block
 from test_framework.script import CScript
 import time
 
 NULLDUMMY_ERROR = "64: non-mandatory-script-verify-flag (Dummy CHECKMULTISIG argument must be zero)"
 
 
 def trueDummy(tx):
     scriptSig = CScript(tx.vin[0].scriptSig)
     newscript = []
     for i in scriptSig:
         if (len(newscript) == 0):
             assert(len(i) == 0)
             newscript.append(b'\x51')
         else:
             newscript.append(i)
     tx.vin[0].scriptSig = CScript(newscript)
     tx.rehash()
 
 
 '''
 This test is meant to exercise NULLDUMMY softfork.
 Connect to a single node.
 Generate 2 blocks (save the coinbases for later).
 Generate 427 more blocks.
 [Policy/Consensus] Check that NULLDUMMY compliant transactions are accepted in the 430th block.
 [Policy] Check that non-NULLDUMMY transactions are rejected before activation.
 [Consensus] Check that the new NULLDUMMY rules are not enforced on the 431st block.
 [Policy/Consensus] Check that the new NULLDUMMY rules are enforced on the 432nd block.
 '''
 
 
 class NULLDUMMYTest(BitcoinTestFramework):
 
     def set_test_params(self):
         self.num_nodes = 1
         self.setup_clean_chain = True
         self.extra_args = [['-whitelist=127.0.0.1']]
 
     def run_test(self):
         self.address = self.nodes[0].getnewaddress()
         self.ms_address = self.nodes[0].addmultisigaddress(1, [self.address])
 
         network_thread_start()
         self.coinbase_blocks = self.nodes[0].generate(2)  # Block 2
         coinbase_txid = []
         for i in self.coinbase_blocks:
             coinbase_txid.append(self.nodes[0].getblock(i)['tx'][0])
         self.nodes[0].generate(427)  # Block 429
         self.lastblockhash = self.nodes[0].getbestblockhash()
         self.tip = int("0x" + self.lastblockhash, 0)
         self.lastblockheight = 429
         self.lastblocktime = int(time.time()) + 429
 
         self.log.info(
             "Test 1: NULLDUMMY compliant base transactions should be accepted to mempool and mined before activation [430]")
         test1txs = [self.create_transaction(
             self.nodes[0], coinbase_txid[0], self.ms_address, 49)]
-        txid1 = self.nodes[0].sendrawtransaction(
-            bytes_to_hex_str(test1txs[0].serialize()), True)
+        txid1 = self.nodes[0].sendrawtransaction(ToHex(test1txs[0]), True)
         test1txs.append(self.create_transaction(
             self.nodes[0], txid1, self.ms_address, 48))
-        txid2 = self.nodes[0].sendrawtransaction(
-            bytes_to_hex_str(test1txs[1].serialize()), True)
+        txid2 = self.nodes[0].sendrawtransaction(ToHex(test1txs[1]), True)
         self.block_submit(self.nodes[0], test1txs, True)
 
         self.log.info(
             "Test 2: Non-NULLDUMMY base multisig transaction should not be accepted to mempool before activation")
         test2tx = self.create_transaction(
             self.nodes[0], txid2, self.ms_address, 48)
         trueDummy(test2tx)
         assert_raises_rpc_error(-26, NULLDUMMY_ERROR,
-                                self.nodes[0].sendrawtransaction, bytes_to_hex_str(test2tx.serialize()), True)
+                                self.nodes[0].sendrawtransaction, ToHex(test2tx), True)
 
         self.log.info(
             "Test 3: Non-NULLDUMMY base transactions should be accepted in a block before activation [431]")
         self.block_submit(self.nodes[0], [test2tx], True)
 
     def create_transaction(self, node, txid, to_address, amount):
         inputs = [{"txid": txid, "vout": 0}]
         outputs = {to_address: amount}
         rawtx = node.createrawtransaction(inputs, outputs)
         signresult = node.signrawtransaction(rawtx)
         return FromHex(CTransaction(), signresult['hex'])
 
     def block_submit(self, node, txs, accept=False):
         block = create_block(self.tip, create_coinbase(
             self.lastblockheight + 1), self.lastblocktime + 1)
         block.nVersion = 4
         for tx in txs:
             tx.rehash()
             block.vtx.append(tx)
         block.vtx = [block.vtx[0]] + \
             sorted(block.vtx[1:], key=lambda tx: tx.get_id())
         block.hashMerkleRoot = block.calc_merkle_root()
         block.rehash()
         block.solve()
-        node.submitblock(bytes_to_hex_str(block.serialize()))
+        node.submitblock(ToHex(block))
         if (accept):
             assert_equal(node.getbestblockhash(), block.hash)
             self.tip = block.sha256
             self.lastblockhash = block.hash
             self.lastblocktime += 1
             self.lastblockheight += 1
         else:
             assert_equal(node.getbestblockhash(), self.lastblockhash)
 
 
 if __name__ == '__main__':
     NULLDUMMYTest().main()