diff --git a/tests/sys/netpfil/pf/nat64.py b/tests/sys/netpfil/pf/nat64.py
--- a/tests/sys/netpfil/pf/nat64.py
+++ b/tests/sys/netpfil/pf/nat64.py
@@ -39,7 +39,7 @@
     }
 
     def vnet3_handler(self, vnet):
-        ToolsHelper.print_output("echo foo | nc -l 1234")
+        ToolsHelper.print_output("echo foo | nc -l 1234 &")
 
     def vnet2_handler(self, vnet):
         ifname = vnet.iface_alias_map["if1"].name
@@ -82,3 +82,23 @@
         assert "S" in tcp.flags
         assert "A" in tcp.flags
 
+    @pytest.mark.require_user("root")
+    def test_udp_port_closed(self):
+        ToolsHelper.print_output("/sbin/route -6 add default 2001:db8::1")
+
+        import scapy.all as sp
+
+        packet = sp.IPv6(dst="64:ff9b::192.0.2.2") \
+            / sp.UDP(dport=1222) / sp.Raw("bar")
+        reply = sp.sr1(packet, timeout=3)
+        print(reply.show())
+
+        # We expect an ICMPv6 error, not a UDP reply
+        assert not reply.getlayer(sp.UDP)
+        icmp = reply.getlayer(sp.ICMPv6DestUnreach)
+        assert icmp
+        assert icmp.type == 1
+        assert icmp.code == 4
+        udp = reply.getlayer(sp.UDPerror)
+        assert udp
+        assert udp.dport == 1222