diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index f534a6a5553e..6a0288d17b7d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5412,7 +5412,7 @@ static int __btrfs_map_block_for_discard(struct btrfs_fs_info *fs_info,
 	}
 
 	offset = logical - em->start;
-	length = min_t(u64, em->len - offset, length);
+	length = min_t(u64, em->start + em->len - logical, length);
 
 	stripe_len = map->stripe_len;
 	/*