diff --git a/test/functional/feature_dersig.py b/test/functional/feature_dersig.py
index c0f2873a4..a2f270620 100755
--- a/test/functional/feature_dersig.py
+++ b/test/functional/feature_dersig.py
@@ -1,145 +1,142 @@
 #!/usr/bin/env python3
 # Copyright (c) 2015-2016 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test BIP66 (DER SIG).
 
 Test that the DERSIG soft-fork activates at (regtest) height 1251.
 """
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
 from test_framework.mininode import *
 from test_framework.blocktools import create_coinbase, create_block
 from test_framework.script import CScript
-from io import BytesIO
 
 DERSIG_HEIGHT = 1251
 
 # Reject codes that we might receive in this test
 REJECT_INVALID = 16
 REJECT_OBSOLETE = 17
 REJECT_NONSTANDARD = 64
 
 # A canonical signature consists of:
 # <30> <total len> <02> <len R> <R> <02> <len S> <S> <hashtype>
 
 
 def unDERify(tx):
     """
     Make the signature in vin 0 of a tx non-DER-compliant,
     by adding padding after the S-value.
     """
     scriptSig = CScript(tx.vin[0].scriptSig)
     newscript = []
     for i in scriptSig:
         if (len(newscript) == 0):
             newscript.append(i[0:-1] + b'\0' + i[-1:])
         else:
             newscript.append(i)
     tx.vin[0].scriptSig = CScript(newscript)
 
 
 def create_transaction(node, coinbase, to_address, amount):
     from_txid = node.getblock(coinbase)['tx'][0]
     inputs = [{"txid": from_txid, "vout": 0}]
     outputs = {to_address: amount}
     rawtx = node.createrawtransaction(inputs, outputs)
     signresult = node.signrawtransaction(rawtx)
-    tx = CTransaction()
-    tx.deserialize(BytesIO(hex_str_to_bytes(signresult['hex'])))
-    return tx
+    return FromHex(CTransaction(), signresult['hex'])
 
 
 class BIP66Test(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 1
         self.extra_args = [
             ['-promiscuousmempoolflags=1', '-whitelist=127.0.0.1']]
         self.setup_clean_chain = True
 
     def run_test(self):
         self.nodes[0].add_p2p_connection(P2PInterface())
 
         network_thread_start()
 
         # wait_for_verack ensures that the P2P connection is fully up.
         self.nodes[0].p2p.wait_for_verack()
 
         self.log.info("Mining %d blocks", DERSIG_HEIGHT - 1)
         self.coinbase_blocks = self.nodes[0].generate(DERSIG_HEIGHT - 1)
         self.nodeaddress = self.nodes[0].getnewaddress()
 
         self.log.info("Test that blocks must now be at least version 3")
         tip = self.nodes[0].getbestblockhash()
         block_time = self.nodes[0].getblockheader(tip)['mediantime'] + 1
         block = create_block(
             int(tip, 16), create_coinbase(DERSIG_HEIGHT), block_time)
         block.nVersion = 2
         block.rehash()
         block.solve()
         self.nodes[0].p2p.send_and_ping(msg_block(block))
         assert_equal(self.nodes[0].getbestblockhash(), tip)
 
         wait_until(lambda: "reject" in self.nodes[0].p2p.last_message.keys(),
                    lock=mininode_lock)
         with mininode_lock:
             assert_equal(
                 self.nodes[0].p2p.last_message["reject"].code, REJECT_OBSOLETE)
             assert_equal(
                 self.nodes[0].p2p.last_message["reject"].reason, b'bad-version(0x00000002)')
             assert_equal(
                 self.nodes[0].p2p.last_message["reject"].data, block.sha256)
             del self.nodes[0].p2p.last_message["reject"]
 
         self.log.info(
             "Test that transactions with non-DER signatures cannot appear in a block")
         block.nVersion = 3
 
         spendtx = create_transaction(self.nodes[0], self.coinbase_blocks[1],
                                      self.nodeaddress, 1.0)
         unDERify(spendtx)
         spendtx.rehash()
 
         # Now we verify that a block with this transaction is invalid.
         block.vtx.append(spendtx)
         block.hashMerkleRoot = block.calc_merkle_root()
         block.rehash()
         block.solve()
 
         self.nodes[0].p2p.send_and_ping(msg_block(block))
         assert_equal(self.nodes[0].getbestblockhash(), tip)
 
         wait_until(lambda: "reject" in self.nodes[0].p2p.last_message.keys(),
                    lock=mininode_lock)
         with mininode_lock:
             # We can receive different reject messages depending on whether
             # bitcoind is running with multiple script check threads. If script
             # check threads are not in use, then transaction script validation
             # happens sequentially, and bitcoind produces more specific reject
             # reasons.
             assert self.nodes[0].p2p.last_message["reject"].code in [
                 REJECT_INVALID, REJECT_NONSTANDARD]
             assert_equal(
                 self.nodes[0].p2p.last_message["reject"].data, block.sha256)
             if self.nodes[0].p2p.last_message["reject"].code == REJECT_INVALID:
                 # Generic rejection when a block is invalid
                 assert_equal(
                     self.nodes[0].p2p.last_message["reject"].reason, b'blk-bad-inputs')
             else:
                 assert b'Non-canonical DER signature' in self.nodes[0].p2p.last_message["reject"].reason
 
         self.log.info(
             "Test that a version 3 block with a DERSIG-compliant transaction is accepted")
         block.vtx[1] = create_transaction(self.nodes[0],
                                           self.coinbase_blocks[1], self.nodeaddress, 1.0)
         block.hashMerkleRoot = block.calc_merkle_root()
         block.rehash()
         block.solve()
 
         self.nodes[0].p2p.send_and_ping(msg_block(block))
         assert_equal(int(self.nodes[0].getbestblockhash(), 16), block.sha256)
 
 
 if __name__ == '__main__':
     BIP66Test().main()