diff --git a/libc/kernel/uapi/linux/mctp.h b/libc/kernel/uapi/linux/mctp.h
index 21a9a14..f02c12f 100644
--- a/libc/kernel/uapi/linux/mctp.h
+++ b/libc/kernel/uapi/linux/mctp.h
@@ -46,5 +46,13 @@
 #define MCTP_ADDR_ANY 0xff
 #define MCTP_TAG_MASK 0x07
 #define MCTP_TAG_OWNER 0x08
+#define MCTP_TAG_PREALLOC 0x10
 #define MCTP_OPT_ADDR_EXT 1
+#define SIOCMCTPALLOCTAG (SIOCPROTOPRIVATE + 0)
+#define SIOCMCTPDROPTAG (SIOCPROTOPRIVATE + 1)
+struct mctp_ioc_tag_ctl {
+  mctp_eid_t peer_addr;
+  __u8 tag;
+  __u16 flags;
+};
 #endif