diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
index 279527c..b39c84d 100644
--- a/copy/xfs_copy.c
+++ b/copy/xfs_copy.c
@@ -654,8 +654,9 @@
 
 	memset(&mbuf, 0, sizeof(xfs_mount_t));
 	libxfs_buftarg_init(&mbuf, xargs.ddev, xargs.logdev, xargs.rtdev);
-	sbp = libxfs_readbuf(mbuf.m_ddev_targp, XFS_SB_DADDR, 1, 0,
-							&xfs_sb_buf_ops);
+	sbp = libxfs_readbuf(mbuf.m_ddev_targp, XFS_SB_DADDR,
+			     1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT),
+			     0, &xfs_sb_buf_ops);
 	sb = &mbuf.m_sb;
 	libxfs_sb_from_disk(sb, XFS_BUF_TO_SBP(sbp));