diff --git a/drivers/st/mmc/stm32_sdmmc2.c b/drivers/st/mmc/stm32_sdmmc2.c
index 6bdd782..1ee3580 100644
--- a/drivers/st/mmc/stm32_sdmmc2.c
+++ b/drivers/st/mmc/stm32_sdmmc2.c
@@ -528,12 +528,12 @@
 	uint32_t data_ctrl = SDMMC_DCTRLR_DTDIR;
 	uint32_t arg_size;
 
-	assert(size != 0U);
+	assert((size != 0U) && (size <= UINT32_MAX));
 
 	if (size > MMC_BLOCK_SIZE) {
 		arg_size = MMC_BLOCK_SIZE;
 	} else {
-		arg_size = size;
+		arg_size = (uint32_t)size;
 	}
 
 	sdmmc2_params.use_dma = plat_sdmmc2_use_dma(base, buf);