diff --git a/sys/dev/ic/ns16550.h b/sys/dev/ic/ns16550.h
index 29b32c5b6ad7..0400f2babdd2 100644
--- a/sys/dev/ic/ns16550.h
+++ b/sys/dev/ic/ns16550.h
@@ -127,7 +127,8 @@
 #define	com_dlbl	com_dll
 #define	com_dlm		1	/* divisor latch high (R/W) */
 #define	com_dlbh	com_dlm
-#define	REG_DL		com_dll
+#define	REG_DLL		com_dll
+#define	REG_DLH		com_dlm
 
 /* 16450 register #7.  Not multiplexed. */
 #define	com_scr		7	/* scratch register (R/W) */
diff --git a/sys/dev/uart/uart_dev_ns8250.c b/sys/dev/uart/uart_dev_ns8250.c
index 6c5af1985ec2..85cfaec2b675 100644
--- a/sys/dev/uart/uart_dev_ns8250.c
+++ b/sys/dev/uart/uart_dev_ns8250.c
@@ -75,7 +75,7 @@ ns8250_delay(struct uart_bas *bas)
 	lcr = uart_getreg(bas, REG_LCR);
 	uart_setreg(bas, REG_LCR, lcr | LCR_DLAB);
 	uart_barrier(bas);
-	divisor = uart_getdreg(bas, REG_DL);
+	divisor = uart_getreg(bas, REG_DLL) | (uart_getreg(bas, REG_DLH) << 8);
 	uart_barrier(bas);
 	uart_setreg(bas, REG_LCR, lcr);
 	uart_barrier(bas);
@@ -199,7 +199,8 @@ ns8250_param(struct uart_bas *bas, int baudrate, int databits, int stopbits,
 			return (EINVAL);
 		uart_setreg(bas, REG_LCR, lcr | LCR_DLAB);
 		uart_barrier(bas);
-		uart_setdreg(bas, REG_DL, divisor);
+		uart_setreg(bas, REG_DLL, divisor & 0xff);
+		uart_setreg(bas, REG_DLH, (divisor >> 8) & 0xff);
 		uart_barrier(bas);
 	}
 
@@ -241,36 +242,22 @@ ns8250_probe(struct uart_bas *bas)
 	if (val & 0xe0)
 		return (ENXIO);
 
-	lcr = uart_getreg(bas, REG_LCR);
-	uart_setreg(bas, REG_LCR, lcr & ~LCR_DLAB);
-	uart_barrier(bas);
-
-	/* Check known 0 bits that depend on !DLAB. */
-	val = uart_getreg(bas, REG_IER);
-	if (val & 0xf0)
-		goto fail;
-
-	uart_setreg(bas, REG_LCR, lcr);
-	uart_barrier(bas);
 	return (0);
-
- fail:
-	uart_setreg(bas, REG_LCR, lcr);
-	uart_barrier(bas);
-	return (ENXIO);
 }
 
 static void
 ns8250_init(struct uart_bas *bas, int baudrate, int databits, int stopbits,
     int parity)
 {
+	u_char	ier;
 
 	if (bas->rclk == 0)
 		bas->rclk = DEFAULT_RCLK;
 	ns8250_param(bas, baudrate, databits, stopbits, parity);
 
 	/* Disable all interrupt sources. */
-	uart_setreg(bas, REG_IER, 0);
+	ier = uart_getreg(bas, REG_IER) & 0xf0;
+	uart_setreg(bas, REG_IER, ier);
 	uart_barrier(bas);
 
 	/* Disable the FIFO (if present). */
@@ -416,7 +403,8 @@ ns8250_bus_attach(struct uart_softc *sc)
 	ns8250_bus_getsig(sc);
 
 	ns8250_clrint(bas);
-	ns8250->ier = IER_EMSC | IER_ERLS | IER_ERXRDY;
+	ns8250->ier = uart_getreg(bas, REG_IER) & 0xf0;
+	ns8250->ier |= IER_EMSC | IER_ERLS | IER_ERXRDY;
 	uart_setreg(bas, REG_IER, ns8250->ier);
 	uart_barrier(bas);
 	return (0);
@@ -426,9 +414,11 @@ static int
 ns8250_bus_detach(struct uart_softc *sc)
 {
 	struct uart_bas *bas;
+	u_char ier;
 
 	bas = &sc->sc_bas;
-	uart_setreg(bas, REG_IER, 0);
+	ier = uart_getreg(bas, REG_IER) & 0xf0;
+	uart_setreg(bas, REG_IER, ier);
 	uart_barrier(bas);
 	ns8250_clrint(bas);
 	return (0);
@@ -529,7 +519,8 @@ ns8250_bus_ioctl(struct uart_softc *sc, int request, intptr_t data)
 		lcr = uart_getreg(bas, REG_LCR);
 		uart_setreg(bas, REG_LCR, lcr | LCR_DLAB);
 		uart_barrier(bas);
-		divisor = uart_getdreg(bas, REG_DL);
+		divisor = uart_getreg(bas, REG_DLL) |
+		    (uart_getreg(bas, REG_DLH) << 8);
 		uart_barrier(bas);
 		uart_setreg(bas, REG_LCR, lcr);
 		uart_barrier(bas);
@@ -600,7 +591,7 @@ ns8250_bus_probe(struct uart_softc *sc)
 {
 	struct uart_bas *bas;
 	int count, delay, error, limit;
-	uint8_t lsr, mcr;
+	uint8_t lsr, mcr, ier;
 
 	bas = &sc->sc_bas;
 
@@ -684,7 +675,8 @@ ns8250_bus_probe(struct uart_softc *sc)
 		    --limit)
 			DELAY(delay);
 		if (limit == 0) {
-			uart_setreg(bas, REG_IER, 0);
+			ier = uart_getreg(bas, REG_IER) & 0xf0;
+			uart_setreg(bas, REG_IER, ier);
 			uart_setreg(bas, REG_MCR, mcr);
 			uart_setreg(bas, REG_FCR, 0);
 			uart_barrier(bas);