diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 99d48081c5ac..c3465204b8d5 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -285,6 +285,14 @@ xfs_iomap_write_direct(
 
 	ASSERT(count_fsb > 0);
 
+	/*
+	 * xfs_bmapi_write() maps at most XFS_MAX_BMBT_EXTLEN blocks in one
+	 * mapping, so don't reserve blocks for more. A pNFS layout range
+	 * comes from a client, and its block count may not even fit the
+	 * 32-bit reservation. The caller maps the rest with a later call.
+	 */
+	count_fsb = min_t(xfs_filblks_t, count_fsb, XFS_MAX_BMBT_EXTLEN);
+
 	resaligned = xfs_aligned_fsb_count(offset_fsb, count_fsb,
 					   xfs_get_extsz_hint(ip));
 	if (unlikely(XFS_IS_REALTIME_INODE(ip))) {