Index: sbin/camcontrol/camcontrol.c
===================================================================
--- sbin/camcontrol/camcontrol.c
+++ sbin/camcontrol/camcontrol.c
@@ -7791,6 +7791,8 @@
 		mmc_d.len = mmc_data_len;
 		mmc_d.data = mmc_data;
 		mmc_d.flags = MMC_DATA_READ;
+		mmc_d.block_size = 0;
+		mmc_d.block_count = 0;
 	} else flags |= CAM_DIR_NONE;
 
 	cam_fill_mmcio(&ccb->mmcio,
Index: sys/cam/mmc/mmc_da.c
===================================================================
--- sys/cam/mmc/mmc_da.c
+++ sys/cam/mmc/mmc_da.c
@@ -889,6 +889,7 @@
 	struct mmc_data d;
 
 	KASSERT(buf_len == 512, ("Buffer for ext csd must be 512 bytes"));
+	memset(&d, 0, sizeof(d));
 	d.data = rawextcsd;
 	d.len = buf_len;
 	d.flags = MMC_DATA_READ;
@@ -1013,6 +1014,7 @@
 	int err;
 
 	memset(res, 0, 64);
+	memset(&mmc_d, 0, sizeof(mmc_d));
 	mmc_d.len = 64;
 	mmc_d.data = res;
 	mmc_d.flags = MMC_DATA_READ;
@@ -1807,6 +1809,7 @@
 		mmcio->cmd.data->data = bp->bio_data;
 		mmcio->cmd.data->len = 512 * count;
 		mmcio->cmd.data->flags = (bp->bio_cmd == BIO_READ ? MMC_DATA_READ : MMC_DATA_WRITE);
+		mmcio->cmd.data->block_count = mmcio->cmd.data->block_size = 0;
 		/* Direct h/w to issue CMD12 upon completion */
 		if (count > 1) {
 			mmcio->cmd.data->flags |= MMC_DATA_MULTI;