diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index bb52923bf5a..52ef05146d8 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -34,7 +34,6 @@ config SERIAL_SUPPORT_INTERRUPT
 config UART_ASYNC_API
 	bool "Enable new asynchronous UART API [EXPERIMENTAL]"
 	depends on SERIAL_SUPPORT_ASYNC
-	select LEGACY_TIMEOUT_API
 	help
 	  This option enables new asynchronous UART API.
 
diff --git a/drivers/serial/uart_nrfx_uart.c b/drivers/serial/uart_nrfx_uart.c
index 514ae023c95..f26b6c502e8 100644
--- a/drivers/serial/uart_nrfx_uart.c
+++ b/drivers/serial/uart_nrfx_uart.c
@@ -443,7 +443,7 @@ static int uart_nrfx_tx_abort(struct device *dev)
 		return -EINVAL;
 	}
 #if	HW_FLOW_CONTROL
-	if (uart0_cb.tx_timeout != K_FOREVER) {
+	if (uart0_cb.tx_timeout != SYS_FOREVER_MS) {
 		k_delayed_work_cancel(&uart0_cb.tx_timeout_work);
 	}
 #endif
@@ -514,7 +514,7 @@ static int uart_nrfx_rx_disable(struct device *dev)
 	}
 
 	uart0_cb.rx_enabled = 0;
-	if (uart0_cb.rx_timeout != K_FOREVER) {
+	if (uart0_cb.rx_timeout != SYS_FOREVER_MS) {
 		k_delayed_work_cancel(&uart0_cb.rx_timeout_work);
 	}
 	nrf_uart_task_trigger(uart0_addr, NRF_UART_TASK_STOPRX);
@@ -584,16 +584,16 @@ static void rx_isr(struct device *dev)
 		uart0_cb.rx_buffer[uart0_cb.rx_counter] =
 			nrf_uart_rxd_get(uart0_addr);
 		uart0_cb.rx_counter++;
-		if (uart0_cb.rx_timeout == K_NO_WAIT) {
+		if (uart0_cb.rx_timeout == 0) {
 			rx_rdy_evt();
-		} else if (uart0_cb.rx_timeout != K_FOREVER) {
+		} else if (uart0_cb.rx_timeout != SYS_FOREVER_MS) {
 			k_delayed_work_submit(&uart0_cb.rx_timeout_work,
-					      uart0_cb.rx_timeout);
+					      K_MSEC(uart0_cb.rx_timeout));
 		}
 	}
 
 	if (uart0_cb.rx_buffer_length == uart0_cb.rx_counter) {
-		if (uart0_cb.rx_timeout != K_FOREVER) {
+		if (uart0_cb.rx_timeout != SYS_FOREVER_MS) {
 			k_delayed_work_cancel(&uart0_cb.rx_timeout_work);
 		}
 		rx_rdy_evt();
@@ -622,9 +622,9 @@ static void tx_isr(void)
 	if (uart0_cb.tx_counter < uart0_cb.tx_buffer_length &&
 	    !uart0_cb.tx_abort) {
 #if	HW_FLOW_CONTROL
-		if (uart0_cb.tx_timeout != K_FOREVER) {
+		if (uart0_cb.tx_timeout != SYS_FOREVER_MS) {
 			k_delayed_work_submit(&uart0_cb.tx_timeout_work,
-					      uart0_cb.tx_timeout);
+					      K_MSEC(uart0_cb.tx_timeout));
 		}
 #endif
 		nrf_uart_event_clear(uart0_addr, NRF_UART_EVENT_TXDRDY);
@@ -635,7 +635,7 @@ static void tx_isr(void)
 	} else {
 #if	HW_FLOW_CONTROL
 
-		if (uart0_cb.tx_timeout != K_FOREVER) {
+		if (uart0_cb.tx_timeout != SYS_FOREVER_MS) {
 			k_delayed_work_cancel(&uart0_cb.tx_timeout_work);
 		}
 #endif
@@ -664,7 +664,7 @@ static void tx_isr(void)
 
 static void error_isr(struct device *dev)
 {
-	if (uart0_cb.rx_timeout != K_FOREVER) {
+	if (uart0_cb.rx_timeout != SYS_FOREVER_MS) {
 		k_delayed_work_cancel(&uart0_cb.rx_timeout_work);
 	}
 	nrf_uart_event_clear(uart0_addr, NRF_UART_EVENT_ERROR);
@@ -741,7 +741,7 @@ static void tx_timeout(struct k_work *work)
 {
 	struct uart_event evt;
 
-	if (uart0_cb.tx_timeout != K_FOREVER) {
+	if (uart0_cb.tx_timeout != SYS_FOREVER_MS) {
 		k_delayed_work_cancel(&uart0_cb.tx_timeout_work);
 	}
 	nrf_uart_task_trigger(uart0_addr, NRF_UART_TASK_STOPTX);
diff --git a/drivers/serial/uart_nrfx_uarte.c b/drivers/serial/uart_nrfx_uarte.c
index 8b864fc955f..cc373871a03 100644
--- a/drivers/serial/uart_nrfx_uarte.c
+++ b/drivers/serial/uart_nrfx_uarte.c
@@ -496,8 +496,8 @@ static int uarte_nrfx_tx(struct device *dev, const u8_t *buf, size_t len,
 			     NRF_UARTE_INT_TXSTOPPED_MASK);
 	nrf_uarte_task_trigger(uarte, NRF_UARTE_TASK_STARTTX);
 	if (data->uart_config.flow_ctrl == UART_CFG_FLOW_CTRL_RTS_CTS
-	    && timeout != K_FOREVER) {
-		k_timer_start(&data->async->tx_timeout_timer, timeout,
+	    && timeout != SYS_FOREVER_MS) {
+		k_timer_start(&data->async->tx_timeout_timer, K_MSEC(timeout),
 			      K_NO_WAIT);
 	}
 	return 0;
@@ -733,11 +733,11 @@ static void rxstarted_isr(struct device *dev)
 		.type = UART_RX_BUF_REQUEST,
 	};
 	user_callback(dev, &evt);
-	if (data->async->rx_timeout != K_FOREVER) {
+	if (data->async->rx_timeout != SYS_FOREVER_MS) {
 		data->async->rx_timeout_left = data->async->rx_timeout;
 		k_timer_start(&data->async->rx_timeout_timer,
-			      data->async->rx_timeout_slab,
-			      data->async->rx_timeout_slab);
+			      K_MSEC(data->async->rx_timeout_slab),
+			      K_MSEC(data->async->rx_timeout_slab));
 	}
 }
 
diff --git a/drivers/serial/uart_sam0.c b/drivers/serial/uart_sam0.c
index b5e4b49b77f..e266b799f3b 100644
--- a/drivers/serial/uart_sam0.c
+++ b/drivers/serial/uart_sam0.c
@@ -354,7 +354,7 @@ static void uart_sam0_rx_timeout(struct k_work *work)
 	if (dev_data->rx_timeout_from_isr) {
 		dev_data->rx_timeout_from_isr = false;
 		k_delayed_work_submit(&dev_data->rx_timeout_work,
-				      dev_data->rx_timeout_chunk);
+				      K_MSEC(dev_data->rx_timeout_chunk));
 		irq_unlock(key);
 		return;
 	}
@@ -375,7 +375,8 @@ static void uart_sam0_rx_timeout(struct k_work *work)
 		u32_t remaining = MIN(dev_data->rx_timeout_time - elapsed,
 				      dev_data->rx_timeout_chunk);
 
-		k_delayed_work_submit(&dev_data->rx_timeout_work, remaining);
+		k_delayed_work_submit(&dev_data->rx_timeout_work,
+				      K_MSEC(remaining));
 	}
 
 	irq_unlock(key);
@@ -839,8 +840,9 @@ static int uart_sam0_tx(struct device *dev, const u8_t *buf, size_t len,
 		return retval;
 	}
 
-	if (timeout != K_FOREVER) {
-		k_delayed_work_submit(&dev_data->tx_timeout_work, timeout);
+	if (timeout != SYS_FOREVER_MS) {
+		k_delayed_work_submit(&dev_data->tx_timeout_work,
+				      K_MSEC(timeout));
 	}
 
 	return dma_start(dev_data->dma, cfg->tx_dma_channel);
diff --git a/include/drivers/uart.h b/include/drivers/uart.h
index 8484574fd63..7d8a6a89aab 100644
--- a/include/drivers/uart.h
+++ b/include/drivers/uart.h
@@ -456,7 +456,7 @@ static inline int uart_callback_set(struct device *dev,
  * @param buf     Pointer to transmit buffer.
  * @param len     Length of transmit buffer.
  * @param timeout Timeout in milliseconds. Valid only if flow control is
- *		  enabled. SYS_FOREVER_MS disables timeout.
+ *		  enabled. @ref SYS_FOREVER_MS disables timeout.
  *
  * @retval -EBUSY There is already an ongoing transfer.
  * @retval 0	  If successful, negative errno code otherwise.
@@ -504,7 +504,7 @@ static inline int z_impl_uart_tx_abort(struct device *dev)
  * @param dev     UART device structure.
  * @param buf     Pointer to receive buffer.
  * @param len     Buffer length.
- * @param timeout Timeout in milliseconds. SYS_FOREVER_MS disables timeout.
+ * @param timeout Timeout in milliseconds. @ref SYS_FOREVER_MS disables timeout.
  *
  * @retval -EBUSY RX already in progress.
  * @retval 0	  If successful, negative errno code otherwise.