diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index e7fa611887ad..8d035842fe51 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5876,7 +5876,7 @@ xfs_bmap_insert_extents(
 	XFS_WANT_CORRUPTED_GOTO(mp, !isnullstartblock(got.br_startblock),
 				del_cursor);
 
-	if (stop_fsb >= got.br_startoff + got.br_blockcount) {
+	if (stop_fsb > got.br_startoff) {
 		ASSERT(0);
 		error = -EFSCORRUPTED;
 		goto del_cursor;
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index d6d78e127625..113bed28bc31 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1167,6 +1167,7 @@ xfs_prepare_shift(
 	struct xfs_inode	*ip,
 	loff_t			offset)
 {
+	struct xfs_mount	*mp = ip->i_mount;
 	int			error;
 
 	/*
@@ -1179,6 +1180,17 @@ xfs_prepare_shift(
 			return error;
 	}
 
+	/*
+	 * Shift operations must stabilize the start block offset boundary along
+	 * with the full range of the operation. If we don't, a COW writeback
+	 * completion could race with an insert, front merge with the start
+	 * extent (after split) during the shift and corrupt the file. Start
+	 * with the block just prior to the start to stabilize the boundary.
+	 */
+	offset = round_down(offset, 1 << mp->m_sb.sb_blocklog);
+	if (offset)
+		offset -= (1 << mp->m_sb.sb_blocklog);
+
 	/*
 	 * Writeback and invalidate cache for the remainder of the file as we're
 	 * about to shift down every extent from offset to EOF.