diff --git a/ports/zephyr/machine_uart.c b/ports/zephyr/machine_uart.c
index 6ae8707d7f..23d7d59443 100644
--- a/ports/zephyr/machine_uart.c
+++ b/ports/zephyr/machine_uart.c
@@ -131,7 +131,7 @@ STATIC mp_uint_t machine_uart_write(mp_obj_t self_in, const void *buf_in, mp_uin
     return size;
 }
 
-STATIC mp_uint_t machine_uart_ioctl(mp_obj_t self_in, mp_uint_t request, mp_uint_t arg, int *errcode) {
+STATIC mp_uint_t machine_uart_ioctl(mp_obj_t self_in, mp_uint_t request, uintptr_t arg, int *errcode) {
     mp_uint_t ret;
 
     if (request == MP_STREAM_POLL) {