diff --git a/libc/kernel/uapi/linux/in6.h b/libc/kernel/uapi/linux/in6.h
index 2eb64d0..8dd3238 100644
--- a/libc/kernel/uapi/linux/in6.h
+++ b/libc/kernel/uapi/linux/in6.h
@@ -134,6 +134,7 @@
 #define IPV6_LEAVE_ANYCAST 28
 #define IPV6_MULTICAST_ALL 29
 #define IPV6_ROUTER_ALERT_ISOLATE 30
+#define IPV6_RECVERR_RFC4884 31
 #define IPV6_PMTUDISC_DONT 0
 #define IPV6_PMTUDISC_WANT 1
 #define IPV6_PMTUDISC_DO 2