diff --git a/test/functional/test_framework/messages.py b/test/functional/test_framework/messages.py
index 7cf51d922..954ae3c4d 100755
--- a/test/functional/test_framework/messages.py
+++ b/test/functional/test_framework/messages.py
@@ -605,7 +605,7 @@ class CBlock(CBlockHeader):
         super(CBlock, self).deserialize(f)
         self.vtx = deser_vector(f, CTransaction)
 
-    def serialize(self, with_witness=False):
+    def serialize(self, with_witness=True):
         r = b""
         r += super(CBlock, self).serialize()
         if with_witness: