diff --git a/tests/unittests/sources/test_vmware.py b/tests/unittests/sources/test_vmware.py
index bcfbfed7ec2a..33193f89f5e1 100644
--- a/tests/unittests/sources/test_vmware.py
+++ b/tests/unittests/sources/test_vmware.py
@@ -90,7 +90,9 @@
 }
 
 
-def generate_test_netdev_data(ipv4=[], ipv6=[]):
+def generate_test_netdev_data(ipv4=None, ipv6=None):
+    ipv4 = ipv4 or []
+    ipv6 = ipv6 or []
     return {
         "eth0": {
             "hwaddr": "00:16:3e:16:db:54",