diff --git a/common/partitions/efi.c b/common/partitions/efi.c
index dcb95414f..61abf0005 100644
--- a/common/partitions/efi.c
+++ b/common/partitions/efi.c
@@ -55,7 +55,7 @@ static u64 last_lba(struct block_device *bdev)
 {
 	if (!bdev)
 		return 0;
-	return bdev->num_blocks;
+	return bdev->num_blocks - 1;
 }
 
 /**