diff --git a/components/drivers/sdio/block_dev.c b/components/drivers/sdio/block_dev.c
index cb1cee732a..f6c705f54c 100644
--- a/components/drivers/sdio/block_dev.c
+++ b/components/drivers/sdio/block_dev.c
@@ -259,7 +259,7 @@ static rt_size_t rt_mmcsd_read(rt_device_t dev,
     rt_sem_take(part->lock, RT_WAITING_FOREVER);
     while (remain_size)
     {
-        req_size = (size > blk_dev->max_req_size) ? blk_dev->max_req_size : remain_size;
+        req_size = (remain_size > blk_dev->max_req_size) ? blk_dev->max_req_size : remain_size;
         err = rt_mmcsd_req_blk(blk_dev->card, part->offset + pos + offset, rd_ptr, req_size, 0);
         if (err)
             break;
@@ -299,7 +299,7 @@ static rt_size_t rt_mmcsd_write(rt_device_t dev,
     rt_sem_take(part->lock, RT_WAITING_FOREVER);
     while (remain_size)
     {
-        req_size = (size > blk_dev->max_req_size) ? blk_dev->max_req_size : remain_size;
+        req_size = (remain_size > blk_dev->max_req_size) ? blk_dev->max_req_size : remain_size;
         err = rt_mmcsd_req_blk(blk_dev->card, part->offset + pos + offset, wr_ptr, req_size, 1);
         if (err)
             break;