diff --git a/src/platforms/common/aux_serial.c b/src/platforms/common/aux_serial.c
index 418751e..bd1f910 100644
--- a/src/platforms/common/aux_serial.c
+++ b/src/platforms/common/aux_serial.c
@@ -20,6 +20,7 @@
 
 #if defined(STM32F0) || defined(STM32F1) || defined(STM32F3) || defined(STM32F4)
 #include <libopencm3/stm32/usart.h>
+#include <libopencm3/stm32/dma.h>
 #elif defined(LM4F)
 #include <libopencm3/lm4f/uart.h>
 #else
@@ -72,3 +73,24 @@ void aux_serial_set_encoding(struct usb_cdc_line_coding *coding)
 		break;
 	}
 }
+
+#if defined(STM32F0) || defined(STM32F1) || defined(STM32F3) || defined(STM32F4)
+/*
+ * Changes USBUSART TX buffer in which data is accumulated from USB.
+ * Filled buffer is submitted to DMA for transfer.
+ */
+void usbuart_change_dma_tx_buf(void)
+{
+	/* Select buffer for transmission */
+	char *const tx_buf_ptr = &buf_tx[buf_tx_act_idx * TX_BUF_SIZE];
+
+	/* Configure DMA */
+	dma_set_memory_address(USBUSART_DMA_BUS, USBUSART_DMA_TX_CHAN, (uintptr_t)tx_buf_ptr);
+	dma_set_number_of_data(USBUSART_DMA_BUS, USBUSART_DMA_TX_CHAN, buf_tx_act_sz);
+	dma_enable_channel(USBUSART_DMA_BUS, USBUSART_DMA_TX_CHAN);
+
+	/* Change active buffer */
+	buf_tx_act_sz = 0;
+	buf_tx_act_idx ^= 1;
+}
+#endif
diff --git a/src/platforms/stm32/usbuart.c b/src/platforms/stm32/usbuart.c
index 2f66803..3d098a5 100644
--- a/src/platforms/stm32/usbuart.c
+++ b/src/platforms/stm32/usbuart.c
@@ -182,25 +182,6 @@ void aux_serial_init(void)
 	usart_enable_rx_dma(USBUSART);
 }
 
-/*
- * Changes USBUSART TX buffer in which data is accumulated from USB.
- * Filled buffer is submitted to DMA for transfer.
- */
-void usbuart_change_dma_tx_buf(void)
-{
-	/* Select buffer for transmission */
-	char *const tx_buf_ptr = &buf_tx[buf_tx_act_idx * TX_BUF_SIZE];
-
-	/* Configure DMA */
-	dma_set_memory_address(USBUSART_DMA_BUS, USBUSART_DMA_TX_CHAN, (uintptr_t)tx_buf_ptr);
-	dma_set_number_of_data(USBUSART_DMA_BUS, USBUSART_DMA_TX_CHAN, buf_tx_act_sz);
-	dma_enable_channel(USBUSART_DMA_BUS, USBUSART_DMA_TX_CHAN);
-
-	/* Change active buffer */
-	buf_tx_act_sz = 0;
-	buf_tx_act_idx ^= 1;
-}
-
 #if defined(USART_ICR)
 #define USBUSART_ISR_TEMPLATE(USART, DMA_IRQ) do {			\
 	nvic_disable_irq(DMA_IRQ);					\