diff --git a/winsup/cygwin/include/cygwin/socket.h b/winsup/cygwin/include/cygwin/socket.h
index 295885256..0360e71e8 100644
--- a/winsup/cygwin/include/cygwin/socket.h
+++ b/winsup/cygwin/include/cygwin/socket.h
@@ -204,6 +204,9 @@ struct OLD_msghdr
 /* Windows-specific flag values returned by recvmsg. */
 #define MSG_BCAST	0x0400		/* Broadcast datagram */
 #define MSG_MCAST	0x0800		/* Multicast datagram */
+/* AF_UNIX specific */
+#define MSG_CMSG_CLOEXEC 0x1000		/* Set O_CLOEXEC on fd's passed via
+					   SCM_RIGHTS */
 
 /* Setsockoptions(2) level. Thanks to BSD these must match IPPROTO_xxx */
 #define SOL_IP		0