diff --git a/qa/rpc-tests/test_framework/mininode.py b/qa/rpc-tests/test_framework/mininode.py
index 3c9821259..fcad43cf6 100755
--- a/qa/rpc-tests/test_framework/mininode.py
+++ b/qa/rpc-tests/test_framework/mininode.py
@@ -44,6 +44,8 @@ BIP0031_VERSION = 60000
 MY_VERSION = 170002  # past bip-31 for ping/pong
 MY_SUBVERSION = "/python-mininode-tester:0.0.1/"
 
+OVERWINTER_VERSION_GROUP_ID = 0x03C48270
+
 MAX_INV_SZ = 50000
 
 
@@ -565,6 +567,7 @@ class CTxOut(object):
 class CTransaction(object):
     def __init__(self, tx=None):
         if tx is None:
+            self.fOverwintered = False
             self.nVersion = 1
             self.vin = []
             self.vout = []
@@ -575,6 +578,7 @@ class CTransaction(object):
             self.sha256 = None
             self.hash = None
         else:
+            self.fOverwintered = tx.fOverwintered
             self.nVersion = tx.nVersion
             self.vin = copy.deepcopy(tx.vin)
             self.vout = copy.deepcopy(tx.vout)
@@ -586,24 +590,46 @@ class CTransaction(object):
             self.hash = None
 
     def deserialize(self, f):
-        self.nVersion = struct.unpack("<i", f.read(4))[0]
+        header = struct.unpack("<I", f.read(4))[0]
+        self.fOverwintered = bool(header >> 31)
+        self.nVersion = header & 0x7FFFFFFF
+        self.nVersionGroupId = (struct.unpack("<I", f.read(4))[0]
+                                if self.fOverwintered else 0)
+
+        isOverwinterV3 = (self.fOverwintered and
+                          self.nVersionGroupId == OVERWINTER_VERSION_GROUP_ID and
+                          self.nVersion == 3)
+
         self.vin = deser_vector(f, CTxIn)
         self.vout = deser_vector(f, CTxOut)
         self.nLockTime = struct.unpack("<I", f.read(4))[0]
+        if isOverwinterV3:
+            self.nExpiryHeight = struct.unpack("<I", f.read(4))[0]
+
         if self.nVersion >= 2:
             self.vjoinsplit = deser_vector(f, JSDescription)
             if len(self.vjoinsplit) > 0:
                 self.joinSplitPubKey = deser_uint256(f)
                 self.joinSplitSig = f.read(64)
+
         self.sha256 = None
         self.hash = None
 
     def serialize(self):
+        header = (int(self.fOverwintered)<<31) | self.nVersion
+        isOverwinterV3 = (self.fOverwintered and
+                          self.nVersionGroupId == OVERWINTER_VERSION_GROUP_ID and
+                          self.nVersion == 3)
+
         r = ""
-        r += struct.pack("<i", self.nVersion)
+        r += struct.pack("<I", header)
+        if self.fOverwintered:
+            r += struct.pack("<I", self.nVersionGroupId)
         r += ser_vector(self.vin)
         r += ser_vector(self.vout)
         r += struct.pack("<I", self.nLockTime)
+        if isOverwinterV3:
+            r += struct.pack("<I", self.nExpiryHeight)
         if self.nVersion >= 2:
             r += ser_vector(self.vjoinsplit)
             if len(self.vjoinsplit) > 0:
@@ -628,8 +654,10 @@ class CTransaction(object):
         return True
 
     def __repr__(self):
-        r = "CTransaction(nVersion=%i vin=%s vout=%s nLockTime=%i" \
-            % (self.nVersion, repr(self.vin), repr(self.vout), self.nLockTime)
+        r = ("CTransaction(fOverwintered=%r nVersion=%i nVersionGroupId=0x%08x "
+             "vin=%s vout=%s nLockTime=%i nExpiryHeight=%i"
+             % (self.fOverwintered, self.nVersion, self.nVersionGroupId,
+                repr(self.vin), repr(self.vout), self.nLockTime, self.nExpiryHeight))
         if self.nVersion >= 2:
             r += " vjoinsplit=%s" % repr(self.vjoinsplit)
             if len(self.vjoinsplit) > 0: