diff --git a/sys/dev/xen/blkfront/blkfront.c b/sys/dev/xen/blkfront/blkfront.c
index 0a75d79b1d2..c193d84b5a2 100644
--- a/sys/dev/xen/blkfront/blkfront.c
+++ b/sys/dev/xen/blkfront/blkfront.c
@@ -170,6 +170,11 @@ xbd_mksegarray(bus_dma_segment_t *segs, int nsegs,
 	int ref;
 
 	while (sg < last_block_sg) {
+		KASSERT(segs->ds_addr % (1 << XBD_SECTOR_SHFT) == 0,
+		    ("XEN disk driver I/O must be sector aligned"));
+		KASSERT(segs->ds_len % (1 << XBD_SECTOR_SHFT) == 0,
+		    ("XEN disk driver I/Os must be a multiple of "
+		    "the sector length"));
 		buffer_ma = segs->ds_addr;
 		fsect = (buffer_ma & PAGE_MASK) >> XBD_SECTOR_SHFT;
 		lsect = fsect + (segs->ds_len  >> XBD_SECTOR_SHFT) - 1;