diff --git a/test/functional/fundrawtransaction.py b/test/functional/fundrawtransaction.py
--- a/test/functional/fundrawtransaction.py
+++ b/test/functional/fundrawtransaction.py
@@ -5,6 +5,7 @@
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
+from test_framework.mininode import CTransaction, FromHex, COIN
 
 
 def get_unspent(listunspent, amount):
@@ -652,11 +653,10 @@
             rawtx, {"feeRate": 2 * min_relay_tx_fee})
         result3 = self.nodes[3].fundrawtransaction(
             rawtx, {"feeRate": 10 * min_relay_tx_fee})
-        result_fee_rate = result['fee'] * 1000 / count_bytes(result['hex'])
         assert_fee_amount(
-            result2['fee'], count_bytes(result2['hex']), 2 * result_fee_rate)
+            result2['fee'], FromHex(CTransaction(), result2['hex']).billable_size(), 2 * min_relay_tx_fee)
         assert_fee_amount(
-            result3['fee'], count_bytes(result3['hex']), 10 * result_fee_rate)
+            result3['fee'], FromHex(CTransaction(), result3['hex']).billable_size(), 10 * min_relay_tx_fee)
 
         #
         # Test address reuse option #
diff --git a/test/functional/test_framework/mininode.py b/test/functional/test_framework/mininode.py
--- a/test/functional/test_framework/mininode.py
+++ b/test/functional/test_framework/mininode.py
@@ -402,6 +402,12 @@
         self.sha256 = None
         self.hash = None
 
+    def billable_size(self):
+        """
+        Returns the size used for billing the against the transaction
+        """
+        return len(self.serialize())
+
     def serialize(self):
         r = b""
         r += struct.pack("<i", self.nVersion)