diff --git a/tstest/natlab/natlab.go b/tstest/natlab/natlab.go
index 8137799b2..0e92f4e2b 100644
--- a/tstest/natlab/natlab.go
+++ b/tstest/natlab/natlab.go
@@ -456,6 +456,7 @@ func (m *Machine) ListenPacket(network, address string) (net.PacketConn, error)
 			return nil, err
 		}
 		if err := m.registerConn6(c); err != nil {
+			m.unregisterConn4(c)
 			return nil, err
 		}
 	case 4: