diff --git a/libc/kernel/uapi/linux/mptcp.h b/libc/kernel/uapi/linux/mptcp.h
index 4a44a90..cf156dd 100644
--- a/libc/kernel/uapi/linux/mptcp.h
+++ b/libc/kernel/uapi/linux/mptcp.h
@@ -99,6 +99,7 @@
   __u64 mptcpi_rcv_nxt;
   __u8 mptcpi_local_addr_used;
   __u8 mptcpi_local_addr_max;
+  __u8 mptcpi_csum_enabled;
 };
 enum mptcp_event_type {
   MPTCP_EVENT_UNSPEC = 0,