diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c
index 2553e05e0725..5f1376578ea3 100644
--- a/drivers/block/null_blk_zoned.c
+++ b/drivers/block/null_blk_zoned.c
@@ -2,8 +2,7 @@
 #include <linux/vmalloc.h>
 #include "null_blk.h"
 
-/* zone_size in MBs to sectors. */
-#define ZONE_SIZE_SHIFT		11
+#define MB_TO_SECTS(mb) (((sector_t)mb * SZ_1M) >> SECTOR_SHIFT)
 
 static inline unsigned int null_zone_no(struct nullb_device *dev, sector_t sect)
 {
@@ -12,7 +11,7 @@ static inline unsigned int null_zone_no(struct nullb_device *dev, sector_t sect)
 
 int null_zone_init(struct nullb_device *dev)
 {
-	sector_t dev_size = (sector_t)dev->size * 1024 * 1024;
+	sector_t dev_capacity_sects;
 	sector_t sector = 0;
 	unsigned int i;
 
@@ -25,9 +24,12 @@ int null_zone_init(struct nullb_device *dev)
 		return -EINVAL;
 	}
 
-	dev->zone_size_sects = dev->zone_size << ZONE_SIZE_SHIFT;
-	dev->nr_zones = dev_size >>
-				(SECTOR_SHIFT + ilog2(dev->zone_size_sects));
+	dev_capacity_sects = MB_TO_SECTS(dev->size);
+	dev->zone_size_sects = MB_TO_SECTS(dev->zone_size);
+	dev->nr_zones = dev_capacity_sects >> ilog2(dev->zone_size_sects);
+	if (dev_capacity_sects & (dev->zone_size_sects - 1))
+		dev->nr_zones++;
+
 	dev->zones = kvmalloc_array(dev->nr_zones, sizeof(struct blk_zone),
 			GFP_KERNEL | __GFP_ZERO);
 	if (!dev->zones)
@@ -55,7 +57,10 @@ int null_zone_init(struct nullb_device *dev)
 		struct blk_zone *zone = &dev->zones[i];
 
 		zone->start = zone->wp = sector;
-		zone->len = dev->zone_size_sects;
+		if (zone->start + dev->zone_size_sects > dev_capacity_sects)
+			zone->len = dev_capacity_sects - zone->start;
+		else
+			zone->len = dev->zone_size_sects;
 		zone->type = BLK_ZONE_TYPE_SEQWRITE_REQ;
 		zone->cond = BLK_ZONE_COND_EMPTY;