diff --git a/test/functional/mempool_reorg.py b/test/functional/mempool_reorg.py
--- a/test/functional/mempool_reorg.py
+++ b/test/functional/mempool_reorg.py
@@ -56,11 +56,13 @@
 
         # Create a transaction which is time-locked to two blocks in the future
         timelock_tx = self.nodes[0].createrawtransaction(
-            [{"txid": coinbase_txids[0], "vout": 0}], {node0_address: 49.99})
-        # Set the time lock
-        timelock_tx = timelock_tx.replace("ffffffff", "11111191", 1)
-        timelock_tx = timelock_tx[:-8] + \
-            hex(self.nodes[0].getblockcount() + 2)[2:] + "000000"
+            inputs=[{
+                "txid": coinbase_txids[0],
+                "vout": 0
+            }],
+            outputs={node0_address: 49.99},
+            locktime=self.nodes[0].getblockcount() + 2,
+        )
         timelock_tx = self.nodes[0].signrawtransactionwithwallet(timelock_tx)[
             "hex"]
         # This will raise an exception because the timelock transaction is too