diff --git a/test/functional/abc-mempool-accept-txn.py b/test/functional/abc-mempool-accept-txn.py
--- a/test/functional/abc-mempool-accept-txn.py
+++ b/test/functional/abc-mempool-accept-txn.py
@@ -67,6 +67,8 @@
     def add_transactions_to_block(self, block, tx_list):
         [tx.rehash() for tx in tx_list]
         block.vtx.extend(tx_list)
+        block.vtx = [block.vtx[0]] + \
+            sorted(block.vtx[1:], key=lambda tx: tx.get_id())
 
     # this is a little handier to use than the version in blocktools.py
     def create_tx(self, spend_tx, n, value, script=CScript([OP_TRUE])):