diff --git a/test/functional/feature_block.py b/test/functional/feature_block.py
index 2dfa568c5b..f4f15d293e 100755
--- a/test/functional/feature_block.py
+++ b/test/functional/feature_block.py
@@ -831,6 +831,7 @@ class FullBlockTest(BitcoinTestFramework):
         self.log.info("Reject a block with a transaction with a duplicate hash of a previous transaction (BIP30)")
         self.move_tip(60)
         b61 = self.next_block(61)
+        b61.vtx[0].nLockTime = 0
         b61.vtx[0].vin[0].scriptSig = DUPLICATE_COINBASE_SCRIPT_SIG
         b61.vtx[0].rehash()
         b61 = self.update_block(61, [])
@@ -853,6 +854,7 @@ class FullBlockTest(BitcoinTestFramework):
         b_spend_dup_cb = self.update_block('spend_dup_cb', [tx])
 
         b_dup_2 = self.next_block('dup_2')
+        b_dup_2.vtx[0].nLockTime = 0
         b_dup_2.vtx[0].vin[0].scriptSig = DUPLICATE_COINBASE_SCRIPT_SIG
         b_dup_2.vtx[0].rehash()
         b_dup_2 = self.update_block('dup_2', [])
diff --git a/test/functional/mining_mainnet.py b/test/functional/mining_mainnet.py
index 1a537cd416..4f95696f78 100755
--- a/test/functional/mining_mainnet.py
+++ b/test/functional/mining_mainnet.py
@@ -30,6 +30,7 @@ from test_framework.blocktools import (
 
 from test_framework.messages import (
     CBlock,
+    SEQUENCE_FINAL,
 )
 
 import json
@@ -61,6 +62,10 @@ class MiningMainnetTest(BitcoinTestFramework):
         block.nBits = DIFF_1_N_BITS
         block.nNonce = blocks['nonces'][height - 1]
         block.vtx = [create_coinbase(height=height, script_pubkey=bytes.fromhex(COINBASE_SCRIPT_PUBKEY), retarget_period=2016)]
+        # The alternate mainnet chain was mined with non-timelocked coinbase txs.
+        block.vtx[0].nLockTime = 0
+        block.vtx[0].vin[0].nSequence = SEQUENCE_FINAL
+        block.vtx[0].rehash()
         block.hashMerkleRoot = block.calc_merkle_root()
         block.rehash()
         block_hex = block.serialize(with_witness=False).hex()
diff --git a/test/functional/test_framework/blocktools.py b/test/functional/test_framework/blocktools.py
index 8e61628557..c36fdb5c76 100644
--- a/test/functional/test_framework/blocktools.py
+++ b/test/functional/test_framework/blocktools.py
@@ -29,6 +29,7 @@ from .messages import (
     tx_from_hex,
     uint256_from_compact,
     WITNESS_SCALE_FACTOR,
+    MAX_SEQUENCE_NONFINAL,
 )
 from .script import (
     CScript,
@@ -151,7 +152,8 @@ def create_coinbase(height, pubkey=None, *, script_pubkey=None, extra_output_scr
     If extra_output_script is given, make a 0-value output to that
     script. This is useful to pad block weight/sigops as needed. """
     coinbase = CTransaction()
-    coinbase.vin.append(CTxIn(COutPoint(0, 0xffffffff), script_BIP34_coinbase_height(height), SEQUENCE_FINAL))
+    coinbase.nLockTime = height - 1
+    coinbase.vin.append(CTxIn(COutPoint(0, 0xffffffff), script_BIP34_coinbase_height(height), MAX_SEQUENCE_NONFINAL))
     coinbaseoutput = CTxOut()
     coinbaseoutput.nValue = nValue * COIN
     if nValue == 50: