diff --git a/include/grub/serial.h b/include/grub/serial.h
index 1c35b4093..758b6fb3e 100644
--- a/include/grub/serial.h
+++ b/include/grub/serial.h
@@ -59,9 +59,15 @@
 #define UART_DLAB	0x80
 
 /* Enable the FIFO.  */
-#define UART_ENABLE_FIFO	0xC7
+#define UART_ENABLE_FIFO_TRIGGER14	0xC7
+
+/* Enable the FIFO.  */
+#define UART_ENABLE_FIFO_TRIGGER1       0x07
 
 /* Turn on DTR, RTS, and OUT2.  */
-#define UART_ENABLE_MODEM	0x0B
+#define UART_ENABLE_DTRRTS	0x03
+
+/* Turn on DTR, RTS, and OUT2.  */
+#define UART_ENABLE_OUT2	0x08
 
 #endif /* ! GRUB_SERIAL_MACHINE_HEADER */
diff --git a/term/serial.c b/term/serial.c
index 05497ce40..2dbebc2f1 100644
--- a/term/serial.c
+++ b/term/serial.c
@@ -300,10 +300,17 @@ serial_hw_init (void)
   /* In Yeeloong serial port has only 3 wires.  */
 #ifndef GRUB_MACHINE_MIPS_YEELOONG
   /* Enable the FIFO.  */
-  grub_outb (UART_ENABLE_FIFO, serial_settings.port + UART_FCR);
+  grub_outb (UART_ENABLE_FIFO_TRIGGER1, serial_settings.port + UART_FCR);
+
+  /* Turn on DTR and RTS.  */
+  grub_outb (UART_ENABLE_DTRRTS, serial_settings.port + UART_MCR);
+#else
+  /* Enable the FIFO.  */
+  grub_outb (UART_ENABLE_FIFO_TRIGGER14, serial_settings.port + UART_FCR);
 
   /* Turn on DTR, RTS, and OUT2.  */
-  grub_outb (UART_ENABLE_MODEM, serial_settings.port + UART_MCR);
+  grub_outb (UART_ENABLE_DTRRTS | UART_ENABLE_OUT2,
+	     serial_settings.port + UART_MCR);
 #endif
 
   /* Drain the input buffer.  */