diff --git a/shared-bindings/wiznet/wiznet5k.c b/shared-bindings/wiznet/wiznet5k.c
index 826783771f..b8382162f0 100644
--- a/shared-bindings/wiznet/wiznet5k.c
+++ b/shared-bindings/wiznet/wiznet5k.c
@@ -66,15 +66,14 @@ STATIC mp_obj_t wiznet5k_make_new(const mp_obj_type_t *type, size_t n_args, cons
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_spi, MP_ARG_REQUIRED | MP_ARG_OBJ },
         { MP_QSTR_cs, MP_ARG_REQUIRED | MP_ARG_OBJ },
-        { MP_QSTR_rst, MP_ARG_REQUIRED | MP_ARG_OBJ },
+        { MP_QSTR_rst, MP_ARG_OBJ, { .u_obj = mp_const_none } },
         { MP_QSTR_dhcp, MP_ARG_KW_ONLY | MP_ARG_BOOL, { .u_bool = true } },
     };
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
     // XXX check type of ARG_spi?
-    // XXX should ARG_rst be optional?
     assert_pin(args[ARG_cs].u_obj, false);
-    assert_pin(args[ARG_rst].u_obj, false);
+    assert_pin(args[ARG_rst].u_obj, true); // may be NULL
 
     mp_obj_t ret = wiznet5k_create(args[ARG_spi].u_obj, args[ARG_cs].u_obj, args[ARG_rst].u_obj);
     if (args[ARG_dhcp].u_bool) wiznet5k_start_dhcp();
diff --git a/shared-module/wiznet/wiznet5k.c b/shared-module/wiznet/wiznet5k.c
index 237f678879..847a134840 100644
--- a/shared-module/wiznet/wiznet5k.c
+++ b/shared-module/wiznet/wiznet5k.c
@@ -364,8 +364,6 @@ mp_obj_t wiznet5k_create(mp_obj_t spi_in, mp_obj_t cs_in, mp_obj_t rst_in) {
     wiznet5k_obj.base.type = (mp_obj_type_t*)&mod_network_nic_type_wiznet5k;
     wiznet5k_obj.cris_state = 0;
     wiznet5k_obj.spi = MP_OBJ_TO_PTR(spi_in);
-    common_hal_digitalio_digitalinout_construct(&wiznet5k_obj.cs, cs_in);
-    common_hal_digitalio_digitalinout_construct(&wiznet5k_obj.rst, rst_in);
     wiznet5k_obj.socket_used = 0;
     wiznet5k_obj.dhcp_socket = -1;
 
@@ -380,13 +378,17 @@ mp_obj_t wiznet5k_create(mp_obj_t spi_in, mp_obj_t cs_in, mp_obj_t rst_in) {
         8 // 8 BITS
     );
 
+    common_hal_digitalio_digitalinout_construct(&wiznet5k_obj.cs, cs_in);
     common_hal_digitalio_digitalinout_switch_to_output(&wiznet5k_obj.cs, 1, DRIVE_MODE_PUSH_PULL);
-    common_hal_digitalio_digitalinout_switch_to_output(&wiznet5k_obj.rst, 1, DRIVE_MODE_PUSH_PULL); 
 
-    common_hal_digitalio_digitalinout_set_value(&wiznet5k_obj.rst, 0);
-    mp_hal_delay_us(10); // datasheet says 2us
-    common_hal_digitalio_digitalinout_set_value(&wiznet5k_obj.rst, 1);
-    mp_hal_delay_ms(160); // datasheet says 150ms
+    if (rst_in) {
+        common_hal_digitalio_digitalinout_construct(&wiznet5k_obj.rst, rst_in);
+        common_hal_digitalio_digitalinout_switch_to_output(&wiznet5k_obj.rst, 1, DRIVE_MODE_PUSH_PULL); 
+        common_hal_digitalio_digitalinout_set_value(&wiznet5k_obj.rst, 0);
+        mp_hal_delay_us(10); // datasheet says 2us
+        common_hal_digitalio_digitalinout_set_value(&wiznet5k_obj.rst, 1);
+        mp_hal_delay_ms(160); // datasheet says 150ms
+    }
 
     reg_wizchip_cris_cbfunc(wiz_cris_enter, wiz_cris_exit);
     reg_wizchip_cs_cbfunc(wiz_cs_select, wiz_cs_deselect);