diff --git a/test/functional/test_framework/netutil.py b/test/functional/test_framework/netutil.py
--- a/test/functional/test_framework/netutil.py
+++ b/test/functional/test_framework/netutil.py
@@ -115,7 +115,7 @@
             max_possible *= 2
         else:
             break
-    namestr = names.tostring()
+    namestr = names.tobytes()
     return [(namestr[i:i + 16].split(b'\0', 1)[0],
              socket.inet_ntoa(namestr[i + 20:i + 24]))
             for i in range(0, outbytes, struct_size)]