diff --git a/ports/atmel-samd/common-hal/busio/UART.c b/ports/atmel-samd/common-hal/busio/UART.c
index 10618d1cec..b4539eb931 100644
--- a/ports/atmel-samd/common-hal/busio/UART.c
+++ b/ports/atmel-samd/common-hal/busio/UART.c
@@ -55,7 +55,7 @@ static void usart_async_rxc_callback(const struct usart_async_descriptor *const
 void common_hal_busio_uart_construct(busio_uart_obj_t *self,
         const mcu_pin_obj_t * tx, const mcu_pin_obj_t * rx, uint32_t baudrate,
         uint8_t bits, uart_parity_t parity, uint8_t stop, mp_float_t timeout,
-        uint8_t receiver_buffer_size) {
+        uint16_t receiver_buffer_size) {
     Sercom* sercom = NULL;
     uint8_t sercom_index = 255; // Unset index
     uint32_t rx_pinmux = 0;
diff --git a/ports/esp8266/common-hal/busio/UART.c b/ports/esp8266/common-hal/busio/UART.c
index f10e3dc555..e72dce639c 100644
--- a/ports/esp8266/common-hal/busio/UART.c
+++ b/ports/esp8266/common-hal/busio/UART.c
@@ -40,7 +40,7 @@ extern UartDevice UartDev;
 void common_hal_busio_uart_construct(busio_uart_obj_t *self,
         const mcu_pin_obj_t * tx, const mcu_pin_obj_t * rx, uint32_t baudrate,
         uint8_t bits, uart_parity_t parity, uint8_t stop, mp_float_t timeout,
-        uint8_t receiver_buffer_size) {
+        uint16_t receiver_buffer_size) {
     if (rx != mp_const_none || tx != &pin_GPIO2) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, translate("Only tx supported on UART1 (GPIO2).")));
     }
diff --git a/ports/nrf/common-hal/busio/UART.c b/ports/nrf/common-hal/busio/UART.c
index 593914afc0..b9e9e55387 100644
--- a/ports/nrf/common-hal/busio/UART.c
+++ b/ports/nrf/common-hal/busio/UART.c
@@ -131,7 +131,7 @@ void uart_reset(void) {
 void common_hal_busio_uart_construct (busio_uart_obj_t *self,
                                       const mcu_pin_obj_t * tx, const mcu_pin_obj_t * rx, uint32_t baudrate,
                                       uint8_t bits, uart_parity_t parity, uint8_t stop, mp_float_t timeout,
-                                      uint8_t receiver_buffer_size) {
+                                      uint16_t receiver_buffer_size) {
     // Find a free UART peripheral.
     self->uarte = NULL;
     for (size_t i = 0 ; i < MP_ARRAY_SIZE(nrfx_uartes); i++) {
diff --git a/shared-bindings/busio/UART.h b/shared-bindings/busio/UART.h
index e171f8bb45..776a996be8 100644
--- a/shared-bindings/busio/UART.h
+++ b/shared-bindings/busio/UART.h
@@ -42,7 +42,7 @@ typedef enum {
 extern void common_hal_busio_uart_construct(busio_uart_obj_t *self,
     const mcu_pin_obj_t * tx, const mcu_pin_obj_t * rx, uint32_t baudrate,
     uint8_t bits, uart_parity_t parity, uint8_t stop, mp_float_t timeout,
-    uint8_t receiver_buffer_size);
+    uint16_t receiver_buffer_size);
 
 extern void common_hal_busio_uart_deinit(busio_uart_obj_t *self);
 extern bool common_hal_busio_uart_deinited(busio_uart_obj_t *self);