diff --git a/06_drivers_gpio_uart/README.md b/06_drivers_gpio_uart/README.md
index 5f91cab4..085636ff 100644
--- a/06_drivers_gpio_uart/README.md
+++ b/06_drivers_gpio_uart/README.md
@@ -40,6 +40,7 @@ Some steps for preparing the SD card differ between RPi3 and RPi4, so be careful
 2. On the card, generate a file named `config.txt` with the following contents:
 
 ```txt
+arm_64bit=1
 init_uart_clock=48000000
 ```
 ### Pi 3