diff --git a/README.md b/README.md
index 9926f92..32a0be9 100644
--- a/README.md
+++ b/README.md
@@ -22,13 +22,17 @@ Run `python uniflash.py -h` to see all parameters. But there are several typical
 
 **Note**: you need to hold a bootkey pressed when connecting the device for it to be detected correctly. This key can vary across devices. Typically it's Call, Soft Left, Soft Right, Center, 9 or #, but it can be anything else.
 
-### SC6531E/F/M
+### SC6531E
 
 This is the default target for UniFlash, FDLs for it are shipped in the repo and you don't need to configure anything else.
 
 For SC6531E, firmware is usually 4MB long, so you just need to run `python uniflash.py dump your-output-file.bin` to dump the firmware image and `python uniflash.py flash your-input-file.bin` to flash it.
 
-For SC6531F or SC6531M where firmware can be larger, you need to pass in the length. As with any integer parameter here, you can pass it in hexadecimal format as well.
+### SC6531F/M
+
+For SC6531F or SC6531M, **only readback is supported as of now, attempts to write flash can make the device unbootable!**
+
+Here, firmware can be larger, so you need to pass in the length. As with any integer parameter here, you can pass it in hexadecimal format as well.
 
 E.g. for CAT B26 (bootkey is `#`) the dumping command is: `python uniflash.py -l 0x6b7000 dump b26.bin`