diff --git a/docs/rp2/quickref.rst b/docs/rp2/quickref.rst
index 11a808c110..8ee467d014 100644
--- a/docs/rp2/quickref.rst
+++ b/docs/rp2/quickref.rst
@@ -187,6 +187,13 @@ Use the :ref:`machine.ADC <machine.ADC>` class::
     adc = ADC(Pin(26))     # create ADC object on ADC pin
     adc.read_u16()         # read value, 0-65535 across voltage range 0.0v - 3.3v
 
+The argument of the constructor ADC specifies either a Pin by number, name of as
+Pin object, or a channel number in the range 0 - 3. If a pin is specified,
+the pin is initialized in high-Z mode. If a channel number is used, the pin
+is not initialized and configuring is left to the user code. After hard reset,
+RP2040 pins operate in current sink mode at about 60µA. If the pin is not
+otherwise configured, that may lead to wrong ADC readings.
+
 Software SPI bus
 ----------------
 
diff --git a/ports/rp2/machine_adc.c b/ports/rp2/machine_adc.c
index e5a428563d..ec77e6f5b9 100644
--- a/ports/rp2/machine_adc.c
+++ b/ports/rp2/machine_adc.c
@@ -73,12 +73,9 @@ static mp_obj_t mp_machine_adc_make_new(const mp_obj_type_t *type, size_t n_args
     bool is_ext = false;
     const machine_pin_obj_t *pin = NULL;
 
-    if (mp_obj_is_int(source)) {
-        // Get and validate channel number.
-        channel = mp_obj_get_int(source);
-        if (ADC_IS_VALID_GPIO(channel)) {
-            channel = ADC_CHANNEL_FROM_GPIO(channel);
-        } else if (!(channel >= 0 && channel <= ADC_CHANNEL_TEMPSENSOR)) {
+    if (mp_obj_is_int(source) && (channel = mp_obj_get_int(source)) <= ADC_CHANNEL_TEMPSENSOR) {
+        // Validate channel number.
+        if (channel < 0) {
             mp_raise_ValueError(MP_ERROR_TEXT("invalid channel"));
         }
     } else {
diff --git a/ports/rp2/machine_uart.c b/ports/rp2/machine_uart.c
index ccbf8f781a..0aa958c962 100644
--- a/ports/rp2/machine_uart.c
+++ b/ports/rp2/machine_uart.c
@@ -367,7 +367,11 @@ static void mp_machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args,
             self->timeout_char = min_timeout_char;
         }
 
-        uart_init(self->uart, self->baudrate);
+        uint32_t new_baudrate = uart_init(self->uart, self->baudrate);
+        uint32_t baudrate_diff = new_baudrate > self->baudrate ? new_baudrate - self->baudrate : self->baudrate - new_baudrate;
+        if (baudrate_diff > (self->baudrate / 50)) {
+            mp_raise_ValueError(MP_ERROR_TEXT("Invalid baud rate"));
+        }
         uart_set_format(self->uart, self->bits, self->stop, self->parity);
         __DSB(); // make sure UARTLCR_H register is written to
         uart_set_fifo_enabled(self->uart, true);