diff --git a/avr_usart.h b/avr_usart.h
index 9328b63..af1865a 100644
--- a/avr_usart.h
+++ b/avr_usart.h
@@ -46,7 +46,7 @@ void init_usart0(void);
 void tx_usart0(unsigned char data);
 unsigned char rx_usart0(void);
 
-void serial0_write();
+void serial0_write(char* buffer, uint8_t write_length);
 void serial0_read(char* buffer, uint8_t buf_length);
 void serial0_set_baud(uint8_t baud);
 void seiral0_enable_timeouts(uint8_t ms);