diff --git a/README.md b/README.md
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+++ b/README.md
@@ -31,6 +31,8 @@ Use a J-Link to debug and program.. If you want to get shady with it, you can fl
 
 ## Using the bootloader
 
-Activate the bootloader by holding down the `PROG` button on the badge while turning on. Use your favorite terminal to connect to the badge using the VCP at `115200-8-N-1`. Send a `firmware.hex` file via XMODEM to update.
+Activate the bootloader by holding down the `PROG` button on the badge while turning on. Use your favorite terminal to connect to the badge using the VCP at `115200-8-N-1`.
+
+Send a `firmware.bin` file via XMODEM to update. Do NOT send `.hex` files, they won't work.
 
 Ensure the firmware you send is built with the bootloader target in mind. The uploaded binary will start at `0x8000800` in Flash.
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