-#define IPPROTO_DCCP 33 /* IANA assigned value */
-#define SOCK_DCCP 6 /* Linux socket type */
-#define SOL_DCCP 269 /* Linux socket level */
-/* Per-connection CCID support (since v2.6.30-rc1) */
-#define DCCP_SOCKOPT_AVAILABLE_CCIDS 12 /* List of supported CCIDs */
-#define DCCP_SOCKOPT_CCID 13 /* Sets both TX/RX CCID */
-#define DCCP_SOCKOPT_TX_CCID 14 /* Set/get the TX CCID */
-#define DCCP_SOCKOPT_RX_CCID 15 /* Set/get the RX CCID */
+#define IPPROTO_DCCP 33 /**< IANA assigned value. */
+#endif
+
+#ifndef SOCK_DCCP
+#define SOCK_DCCP 6 /**< Linux socket type. */
+#endif
+
+#ifndef DCCP_SOCKOPT_RX_CCID
+/** Per-connection CCID support (set/get the RX CCID, since v2.6.30-rc1). */
+#define DCCP_SOCKOPT_RX_CCID 15
+#endif
+
+#ifndef SOL_DCCP
+#define SOL_DCCP 269 /**< Linux socket level. */
+#endif
+
+#ifndef DCCP_SOCKOPT_GET_CUR_MPS
+#define DCCP_SOCKOPT_GET_CUR_MPS 5 /**< Max packet size, RFC 4340, 14. */
+#endif
+
+#ifndef DCCP_SOCKOPT_AVAILABLE_CCIDS
+#define DCCP_SOCKOPT_AVAILABLE_CCIDS 12 /**< List of supported CCIDs. */