diff --git a/components/drivers/sdio/mmc.c b/components/drivers/sdio/mmc.c
index 5c7ddcb258..34e91ea386 100644
--- a/components/drivers/sdio/mmc.c
+++ b/components/drivers/sdio/mmc.c
@@ -182,6 +182,8 @@ static int mmc_get_ext_csd(struct rt_mmcsd_card *card, rt_uint8_t **new_ext_csd)
  */
 static int mmc_parse_ext_csd(struct rt_mmcsd_card *card, rt_uint8_t *ext_csd)
 {
+  rt_uint64_t card_capacity = 0;
+
   if(card == RT_NULL || ext_csd == RT_NULL)
   {
     LOG_E("emmc parse ext csd fail, invaild args");
@@ -191,9 +193,10 @@ static int mmc_parse_ext_csd(struct rt_mmcsd_card *card, rt_uint8_t *ext_csd)
   card->flags |=  CARD_FLAG_HIGHSPEED;
   card->hs_max_data_rate = 200000000;
   
-  card->card_capacity = *((rt_uint32_t *)&ext_csd[EXT_CSD_SEC_CNT]);
-  card->card_capacity *= card->card_blksize;
-  card->card_capacity >>= 10; /* unit:KB */
+  card_capacity = *((rt_uint32_t *)&ext_csd[EXT_CSD_SEC_CNT]);
+  card_capacity *= card->card_blksize;
+  card_capacity >>= 10; /* unit:KB */
+  card->card_capacity = card_capacity;
   LOG_I("emmc card capacity %d KB.", card->card_capacity);
   
   return 0;