diff --git a/test/functional/mempool_accept.py b/test/functional/mempool_accept.py
index ee9ca9204..57a059b7f 100755
--- a/test/functional/mempool_accept.py
+++ b/test/functional/mempool_accept.py
@@ -92,7 +92,7 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
         tx.deserialize(BytesIO(hex_str_to_bytes(raw_tx_0)))
         txid_0 = tx.rehash()
         self.check_mempool_result(
-            result_expected=[{'txid': txid_0, 'allowed': True, 'vsize': 110, 'fees': {'base': Decimal(str(fee))}}],
+            result_expected=[{'txid': txid_0, 'allowed': True, 'vsize': tx.get_vsize(), 'fees': {'base': Decimal(str(fee))}}],
             rawtxs=[raw_tx_0],
         )
 
@@ -107,7 +107,7 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
         tx.deserialize(BytesIO(hex_str_to_bytes(raw_tx_final)))
         fee_expected = int(coin['amount']) - output_amount
         self.check_mempool_result(
-            result_expected=[{'txid': tx.rehash(), 'allowed': True, 'vsize': 188, 'fees': {'base': Decimal(str(fee_expected))}}],
+            result_expected=[{'txid': tx.rehash(), 'allowed': True, 'vsize': tx.get_vsize(), 'fees': {'base': Decimal(str(fee_expected))}}],
             rawtxs=[tx.serialize().hex()],
             maxfeerate=0,
         )
@@ -130,7 +130,7 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
         tx.deserialize(BytesIO(hex_str_to_bytes(raw_tx_0)))
         txid_0 = tx.rehash()
         self.check_mempool_result(
-            result_expected=[{'txid': txid_0, 'allowed': True, 'vsize': 110, 'fees': {'base': Decimal(str(2 * fee))}}],
+            result_expected=[{'txid': txid_0, 'allowed': True, 'vsize': tx.get_vsize(), 'fees': {'base': Decimal(str(2 * fee))}}],
             rawtxs=[raw_tx_0],
         )
 
@@ -190,7 +190,7 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
         tx.deserialize(BytesIO(hex_str_to_bytes(raw_tx_reference)))
         # Reference tx should be valid on itself
         self.check_mempool_result(
-            result_expected=[{'txid': tx.rehash(), 'allowed': True, 'vsize': 110, 'fees': { 'base': Decimal(str(0.1 - 0.05))}}],
+            result_expected=[{'txid': tx.rehash(), 'allowed': True, 'vsize': tx.get_vsize(), 'fees': { 'base': Decimal(str(0.1 - 0.05))}}],
             rawtxs=[tx.serialize().hex()],
             maxfeerate=0,
         )
diff --git a/test/functional/p2p_segwit.py b/test/functional/p2p_segwit.py
index 1d99761e1..dfbf5d52f 100755
--- a/test/functional/p2p_segwit.py
+++ b/test/functional/p2p_segwit.py
@@ -696,13 +696,13 @@ class SegWitTest(BitcoinTestFramework):
         if not self.segwit_active:
             # Just check mempool acceptance, but don't add the transaction to the mempool, since witness is disallowed
             # in blocks and the tx is impossible to mine right now.
-            assert_equal(self.nodes[0].testmempoolaccept([tx3.serialize_with_witness().hex()]), [{'txid': tx3.hash, 'allowed': True, 'vsize': 93, 'fees': { 'base': Decimal('0.00001000')}}])
+            assert_equal(self.nodes[0].testmempoolaccept([tx3.serialize_with_witness().hex()]), [{'txid': tx3.hash, 'allowed': True, 'vsize': tx3.get_vsize(), 'fees': { 'base': Decimal('0.00001000')}}])
             # Create the same output as tx3, but by replacing tx
             tx3_out = tx3.vout[0]
             tx3 = tx
             tx3.vout = [tx3_out]
             tx3.rehash()
-            assert_equal(self.nodes[0].testmempoolaccept([tx3.serialize_with_witness().hex()]), [{'txid': tx3.hash, 'allowed': True, 'vsize': 93, 'fees': { 'base': Decimal('0.00011000')}}])
+            assert_equal(self.nodes[0].testmempoolaccept([tx3.serialize_with_witness().hex()]), [{'txid': tx3.hash, 'allowed': True, 'vsize': tx3.get_vsize(), 'fees': { 'base': Decimal('0.00011000')}}])
         test_transaction_acceptance(self.nodes[0], self.test_node, tx3, with_witness=True, accepted=True)
 
         self.nodes[0].generate(1)
diff --git a/test/functional/test_framework/messages.py b/test/functional/test_framework/messages.py
index b4e609df3..1e062ab9a 100755
--- a/test/functional/test_framework/messages.py
+++ b/test/functional/test_framework/messages.py
@@ -22,6 +22,7 @@ from codecs import encode
 import copy
 import hashlib
 from io import BytesIO
+import math
 import random
 import socket
 import struct
@@ -67,6 +68,8 @@ MSG_WITNESS_TX = MSG_TX | MSG_WITNESS_FLAG
 
 FILTER_TYPE_BASIC = 0
 
+WITNESS_SCALE_FACTOR = 4
+
 # Serialization/deserialization tools
 def sha256(s):
     return hashlib.new('sha256', s).digest()
@@ -537,6 +540,13 @@ class CTransaction:
                 return False
         return True
 
+    # Calculate the virtual transaction size using witness and non-witness
+    # serialization size (does NOT use sigops).
+    def get_vsize(self):
+        with_witness_size = len(self.serialize_with_witness())
+        without_witness_size = len(self.serialize_without_witness())
+        return math.ceil(((WITNESS_SCALE_FACTOR - 1) * without_witness_size + with_witness_size) / WITNESS_SCALE_FACTOR)
+
     def __repr__(self):
         return "CTransaction(nVersion=%i vin=%s vout=%s wit=%s nLockTime=%i)" \
             % (self.nVersion, repr(self.vin), repr(self.vout), repr(self.wit), self.nLockTime)