diff --git a/libc/kernel/uapi/linux/mptcp.h b/libc/kernel/uapi/linux/mptcp.h
index 67b0ce3..7b3acd5 100644
--- a/libc/kernel/uapi/linux/mptcp.h
+++ b/libc/kernel/uapi/linux/mptcp.h
@@ -77,6 +77,7 @@
 #define MPTCP_PM_ADDR_FLAG_SUBFLOW (1 << 1)
 #define MPTCP_PM_ADDR_FLAG_BACKUP (1 << 2)
 #define MPTCP_PM_ADDR_FLAG_FULLMESH (1 << 3)
+#define MPTCP_PM_ADDR_FLAG_IMPLICIT (1 << 4)
 enum {
   MPTCP_PM_CMD_UNSPEC,
   MPTCP_PM_CMD_ADD_ADDR,