diff --git a/test/functional/rawtransactions.py b/test/functional/rawtransactions.py
index 116b6ab4b..13c34c74e 100755
--- a/test/functional/rawtransactions.py
+++ b/test/functional/rawtransactions.py
@@ -1,6 +1,3 @@
-
-
-
 #!/usr/bin/env python3
 # Copyright (c) 2014-2016 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
diff --git a/test/functional/test_framework/mininode.py b/test/functional/test_framework/mininode.py
index 2bb7ab6f1..9989fb492 100755
--- a/test/functional/test_framework/mininode.py
+++ b/test/functional/test_framework/mininode.py
@@ -434,7 +434,7 @@ class CTransaction(object):
             self.nLockTime = 0
             self.sha256 = None
             self.hash = None
-            self.txComment = ""
+            self.txComment = b""
         else:
             self.nVersion = tx.nVersion
             self.vin = copy.deepcopy(tx.vin)
@@ -443,7 +443,7 @@ class CTransaction(object):
             self.sha256 = tx.sha256
             self.hash = tx.hash
             self.wit = copy.deepcopy(tx.wit)
-            self.txComment = '%s' % tx.txComment
+            self.txComment = b'%s' % tx.txComment
 
     def deserialize(self, f):
         self.nVersion = struct.unpack("<i", f.read(4))[0]
@@ -463,11 +463,7 @@ class CTransaction(object):
             self.wit.deserialize(f)
         self.nLockTime = struct.unpack("<I", f.read(4))[0]
         if self.nVersion >= 2:
-            tx_comment_len = deser_compact_size(f)
-            if tx_comment_len > 0:
-                self.txComment = struct.unpack("<s", f.read(tx_comment_len))[0]
-            else:
-                self.txComment = ""
+            self.txComment = deser_string(f)
         self.sha256 = None
         self.hash = None
 
@@ -478,10 +474,7 @@ class CTransaction(object):
         r += ser_vector(self.vout)
         r += struct.pack("<I", self.nLockTime)
         if self.nVersion >= 2:
-            r += ser_compact_size(len(self.txComment))
-            if len(self.txComment) > 0:
-                r += struct.pack("<s", self.txComment)
-
+            r += ser_string(self.txComment)
         return r
 
     # Only serialize with witness when explicitly called for
@@ -506,10 +499,7 @@ class CTransaction(object):
             r += self.wit.serialize()
         r += struct.pack("<I", self.nLockTime)
         if self.nVersion >= 2:
-            r += ser_compact_size(len(self.txComment))
-            if len(self.txComment) > 0:
-                r += struct.pack("<s", self.txComment)
-        
+            r += ser_string(self.txComment)
         return r
 
     # Regular serialization is without witness -- must explicitly
diff --git a/test/functional/test_framework/script.py b/test/functional/test_framework/script.py
index f1e19df4b..e9af58f6f 100755
--- a/test/functional/test_framework/script.py
+++ b/test/functional/test_framework/script.py
@@ -936,8 +936,6 @@ def SegwitVersion1SignatureHash(script, txTo, inIdx, hashtype, amount):
     ss += struct.pack("<i", txTo.nLockTime)
     ss += struct.pack("<I", hashtype)
     if txTo.nVersion >= 2:
-        ss += ser_compact_size(len(txTo.txComment))
-        if len(txTo.txComment) > 0:
-            ss += struct.pack("<s", txTo.txComment)
+        ss += ser_string(txTo.txComment)
 
     return hash256(ss)