diff --git a/src/udev/udev-builtin-net_id.c b/src/udev/udev-builtin-net_id.c
index d9d395cb2f..65e003eb15 100644
--- a/src/udev/udev-builtin-net_id.c
+++ b/src/udev/udev-builtin-net_id.c
@@ -1018,7 +1018,7 @@ static int builtin_net_id(sd_device *dev, sd_netlink **rtnl, int argc, char *arg
         if (names_mac(dev, &info) >= 0) {
                 char str[ALTIFNAMSIZ];
 
-                xsprintf(str, "%s%s", prefix, HW_ADDR_TO_STR_FULL(&info.hw_addr, HW_ADDR_TO_STRING_NO_COLON));
+                xsprintf(str, "%sx%s", prefix, HW_ADDR_TO_STR_FULL(&info.hw_addr, HW_ADDR_TO_STRING_NO_COLON));
                 udev_builtin_add_property(dev, test, "ID_NET_NAME_MAC", str);
                 log_device_debug(dev, "MAC address identifier: hw_addr=%s → %s",
                                  HW_ADDR_TO_STR(&info.hw_addr), str + strlen(prefix));