diff --git a/hello_uart_async/uart.h b/hello_uart_async/uart.h
index 3c2e1fa..20ed356 100644
--- a/hello_uart_async/uart.h
+++ b/hello_uart_async/uart.h
@@ -3,6 +3,9 @@ int uart_getchar(FILE *stream);
 
 void uart_init(void);
 
+struct rx_ring;
+struct tx_ring;
+
 /* http://www.ermicro.com/blog/?p=325 */
 
 FILE uart_output = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);
diff --git a/hello_uart_async/uart_async.c b/hello_uart_async/uart_async.c
index 1447a24..a9af484 100644
--- a/hello_uart_async/uart_async.c
+++ b/hello_uart_async/uart_async.c
@@ -1,3 +1,5 @@
+/* Based on Atmel Application Note AVR 306 */
+
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <stdio.h>
@@ -33,6 +35,13 @@ static struct rx_ring rx_buffer;
 /* http://www.cs.mun.ca/~rod/Winter2007/4723/notes/serial/serial.html */
 
 void uart_init(void) {
+    
+    tx_buffer.start = 0;
+    tx_buffer.end   = 0;
+
+    rx_buffer.start = 0;
+    rx_buffer.end   = 0;
+    
     UBRR0H = UBRRH_VALUE;
     UBRR0L = UBRRL_VALUE;
 
@@ -80,7 +89,7 @@ ISR(USART_RX_vect) {
 ISR(USART_UDRE_vect){
     int read_pointer = (tx_buffer.start + 1) % UART_TX_BUFFER_SIZE;
     
-    /* Transit next byte if data available in ringbuffer. */
+    /* Transmit next byte if data available in ringbuffer. */
     if (read_pointer != tx_buffer.end) {
         UDR0 = tx_buffer.buffer[read_pointer];
         tx_buffer.start = read_pointer;