diff --git a/kernel/serial.h b/kernel/serial.h
index 955a4f7..cfaad95 100644
--- a/kernel/serial.h
+++ b/kernel/serial.h
@@ -9,7 +9,8 @@ See the file LICENSE for details.
 
 void serial_init();
 
-char serial_read(int port_no);
+int serial_read(int port_no);
+int serial_read_nonblock(int port_no);
 void serial_write(int port_no, char a);
 
 int serial_device_probe( int unit, int *blocksize, int *nblocks, char *info );