diff --git a/bsp/stm32/libraries/HAL_Drivers/drv_usart.c b/bsp/stm32/libraries/HAL_Drivers/drv_usart.c
index 2950266b3c30d75f367e27a56d7cbbf5dba3f7b5..039d008341cba656969f76ba727659edb870a96b 100644
--- a/bsp/stm32/libraries/HAL_Drivers/drv_usart.c
+++ b/bsp/stm32/libraries/HAL_Drivers/drv_usart.c
@@ -634,11 +634,13 @@ void LPUART1_DMA_RX_IRQHandler(void)
 #ifdef RT_SERIAL_USING_DMA
 static void stm32_dma_config(struct rt_serial_device *serial, rt_ubase_t flag)
 {
-    RT_ASSERT(serial != RT_NULL);
     struct rt_serial_rx_fifo *rx_fifo
     DMA_HandleTypeDef *DMA_Handle;
     struct dma_config *dma_config;
-    struct stm32_uart *uart = (struct stm32_uart *)serial->parent.user_data;
+    struct stm32_uart *uart;
+    
+    RT_ASSERT(serial != RT_NULL);
+    uart = (struct stm32_uart *)serial->parent.user_data;
     RT_ASSERT(uart != RT_NULL);
 
     if (RT_DEVICE_FLAG_DMA_RX == flag)