diff --git a/hw/sd/sdhci.c b/hw/sd/sdhci.c
index ed717ab549..c849c3d99b 100644
--- a/hw/sd/sdhci.c
+++ b/hw/sd/sdhci.c
@@ -1107,7 +1107,7 @@ sdhci_write(void *opaque, hwaddr offset, uint64_t val, unsigned size)
         break;
     case SDHC_BLKSIZE:
         if (!TRANSFERRING_DATA(s->prnsts)) {
-            MASKED_WRITE(s->blksize, mask, value);
+            MASKED_WRITE(s->blksize, mask, extract32(value, 0, 12));
             MASKED_WRITE(s->blkcnt, mask >> 16, value >> 16);
         }