diff --git a/Misc/NEWS.d/next/Library/2018-10-13-19-15-23.bpo-34521.YPaiTK.rst b/Misc/NEWS.d/next/Library/2018-10-13-19-15-23.bpo-34521.YPaiTK.rst
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+Use :func:`socket.CMSG_SPACE` to calculate ancillary data size instead of
+:func:`socket.CMSG_LEN` in :func:`multiprocessing.reduction.recvfds` as
+:rfc:`3542` requires the use of the former for portable applications.