2 files changed, 6 insertions, 2 deletions
diff --git a/test/functional/test_framework/messages.py b/test/functional/test_framework/messages.py
index 89a5a65e64..917efaa833 100755
--- a/test/functional/test_framework/messages.py
+++ b/test/functional/test_framework/messages.py
@@ -803,7 +803,9 @@ class HeaderAndShortIDs:
         return [ key0, key1 ]
 
     # Version 2 compact blocks use wtxid in shortids (rather than txid)
-    def initialize_from_block(self, block, nonce=0, prefill_list = [0], use_witness = False):
+    def initialize_from_block(self, block, nonce=0, prefill_list=None, use_witness=False):
+        if prefill_list is None:
+            prefill_list = [0]
         self.header = CBlockHeader(block)
         self.nonce = nonce
         self.prefilled_txn = [ PrefilledTransaction(i, block.vtx[i]) for i in prefill_list ]
diff --git a/test/functional/wallet_importmulti.py b/test/functional/wallet_importmulti.py
index e4a4ab1f35..23748e5dd7 100755
--- a/test/functional/wallet_importmulti.py
+++ b/test/functional/wallet_importmulti.py
@@ -44,8 +44,10 @@ class ImportMultiTest(BitcoinTestFramework):
     def setup_network(self):
         self.setup_nodes()
 
-    def test_importmulti(self, req, success, error_code=None, error_message=None, warnings=[]):
+    def test_importmulti(self, req, success, error_code=None, error_message=None, warnings=None):
         """Run importmulti and assert success"""
+        if warnings is None:
+            warnings = []
         result = self.nodes[1].importmulti([req])
         observed_warnings = []
         if 'warnings' in result[0]: