diff --git a/serial/serial.c b/serial/serial.c
index c4d52e3..f33a29f 100644
--- a/serial/serial.c
+++ b/serial/serial.c
@@ -62,7 +62,7 @@ fprintf(stderr, ">>> %s ( %s %d )\n", __func__, port, baudrate);
 // shall not cause the terminal device to become the controlling terminal
 // for the process.
 
-uart0 = open(port, O_RDONLY | O_NOCTTY);
+uart0 = open(port, O_RDWR | O_NOCTTY);
 if (uart0 < 0)
 	{
 	perror("unable to open uart ");