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Upload error · esptool

Fix “Failed to set baud rate 921600. The driver may not support this rate.”

The USB-serial driver rejected the high upload speed. Set Upload Speed to 115200 or 460800, or update the CH340/PL2303 driver.

ESP32ESP8266ESP32-CAMESP-01Updated 3 Nov 2026

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What you see

OutputOutput
esptool.py v4.8.1
Serial port COM6
Connecting....
Chip is ESP32-D0WD-V3 (revision v3.1)
Uploading stub...
Running stub...
Stub running...
Changing baud rate to 921600

A fatal error occurred: Failed to set baud rate 921600. The driver may not support this rate.
Failed uploading: uploading error: exit status 2

esptool starts every upload at 115200 baud, then asks the operating system to switch to the faster Upload Speed. This error means the driver behind the COM port refused that rate.

Choose a lower Upload Speed and the upload works. Updating the USB-serial driver usually brings back 921600.

Quick fix — try in order

  1. 1

    Lower Upload Speed

    Tools → Upload Speed → 460800 or 115200. On the command line use -b 115200. Uploads take a few seconds longer and work.

  2. 2

    Update the driver

    Old CH340 drivers and the legacy PL2303 driver can't set 921600. Install the current WCH or Silicon Labs driver (links below).

  3. 3

    Virtual and wireless ports can't do it

    Bluetooth serial ports, RFC2217 network ports and some USB-over-network setups (WSL usbipd) only support standard rates. Use 115200 there.

Why it happens

Why does esptool change the baud rate?

It connects at 115200, then switches to the Upload Speed you chose to write faster. If the driver refuses the new rate, esptool can't continue.

PL2303 and FTDI clone adapters

Old adapters often max out at 460800 or lower. See also PL2303HXA phased out.

Board-specific notes

ESP-01 with USB-TTL adapter: 115200 is the safe choice for these setups.

Drivers — official sources only

CP210x (Silicon Labs)silabs.comCH340 / CH341 (WCH)wch-ic.com

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