diff --git a/avr/modules/flash/io_uart_all_attn.asm b/avr/modules/flash/io_uart_all_attn.asm
index 4918dfd..0fd500c 100644
--- a/avr/modules/flash/io_uart_all_attn.asm
+++ b/avr/modules/flash/io_uart_all_attn.asm
@@ -324,9 +324,9 @@ ioRawRecvMsg:
   ; read first two bytes
   ldi r17, 2                    ; 2 bytes: address byte, msg len
   add r19, r17
-  rcall ioRawRecvBytes          ; (r16, r17, r18, r22)
+  rcall ioRawRecvBytes          ; (r16, r17, r20, r22)
   brcc ioRawRecvMsg_error
-  cp r16, r20                   ; check size
+  cp r16, r18                   ; check size
   brcc ioRawRecvMsg_error
   inc r16                       ; account for checksum byte
   ; read remaining bytes including checksum byte