diff --git a/components/esp_driver_uart/src/uart.c b/components/esp_driver_uart/src/uart.c
index 851aee4194f..2f08241e96f 100644
--- a/components/esp_driver_uart/src/uart.c
+++ b/components/esp_driver_uart/src/uart.c
@@ -1638,7 +1638,8 @@ static int uart_tx_all(uart_port_t uart_num, const char *src, size_t size, bool
         }
         xRingbufferSend(p_uart_obj[uart_num]->tx_ring_buf, (void *) &evt, sizeof(uart_tx_data_t), portMAX_DELAY);
         while (size > 0) {
-            size_t send_size = MIN(size, xRingbufferGetCurFreeSize(p_uart_obj[uart_num]->tx_ring_buf));
+            size_t free_size = xRingbufferGetCurFreeSize(p_uart_obj[uart_num]->tx_ring_buf);
+            size_t send_size = MIN(size, free_size);
             if (send_size > 0) {
                 xRingbufferSend(p_uart_obj[uart_num]->tx_ring_buf, (void *)(src + offset), send_size, portMAX_DELAY);
                 size -= send_size;