diff --git a/extmod/network_lwip.c b/extmod/network_lwip.c
index 97cb43902d..329a45c46f 100644
--- a/extmod/network_lwip.c
+++ b/extmod/network_lwip.c
@@ -297,20 +297,23 @@ mp_obj_t mod_network_nic_ipconfig(struct netif *netif, size_t n_args, const mp_o
                             char plain_ip[IPADDR_STRLEN_MAX];
                             char *split = strchr(input_str, '/');
                             const char *addr_str = input_str;
+                            int to_copy = MIN(sizeof(plain_ip) - 1, addr_len);
+                            memcpy(plain_ip, addr_str, to_copy);
                             if (split) {
-                                int to_copy = sizeof(plain_ip) - 1;
                                 if (split - addr_str < to_copy) {
                                     to_copy = split - addr_str;
                                 }
-                                memcpy(plain_ip, addr_str, to_copy);
                                 mp_obj_t prefix_obj = mp_parse_num_integer(split + 1, strlen(split + 1), 10, NULL);
                                 prefix_bits = mp_obj_get_int(prefix_obj);
+                                if (mp_obj_str_get_qstr(args[0]) == MP_QSTR_addr4) {
+                                    uint32_t mask = -(1u << (32 - prefix_bits));
+                                    ip_addr_set_ip4_u32_val(netmask, ((mask & 0xFF) << 24) | ((mask & 0xFF00) << 8) | ((mask >> 8) & 0xFF00) | ((mask >> 24) & 0xFF));
+                                }
+                            } else {
+                                netmask = netif->netmask;
                             }
-                            if (mp_obj_str_get_qstr(args[0]) == MP_QSTR_addr4) {
-                                uint32_t mask = -(1u << (32 - prefix_bits));
-                                ip_addr_set_ip4_u32_val(netmask, ((mask & 0xFF) << 24) | ((mask & 0xFF00) << 8) | ((mask >> 8) & 0xFF00) | ((mask >> 24) & 0xFF));
-                            }
-                            if (!ipaddr_aton(addr_str, &ip_addr)) {
+                            plain_ip[to_copy] = '\0';
+                            if (!ipaddr_aton(plain_ip, &ip_addr)) {
                                 mp_raise_ValueError(MP_ERROR_TEXT("invalid arguments"));
                             }
                             if ((mp_obj_str_get_qstr(args[0]) == MP_QSTR_addr6) != IP_IS_V6(&ip_addr)