diff --git a/libc/kernel/uapi/linux/in.h b/libc/kernel/uapi/linux/in.h
index 99b54cc..e5437ca 100644
--- a/libc/kernel/uapi/linux/in.h
+++ b/libc/kernel/uapi/linux/in.h
@@ -112,6 +112,7 @@
 #define IP_CHECKSUM 23
 #define IP_BIND_ADDRESS_NO_PORT 24
 #define IP_RECVFRAGSIZE 25
+#define IP_RECVERR_RFC4884 26
 #define IP_PMTUDISC_DONT 0
 #define IP_PMTUDISC_WANT 1
 #define IP_PMTUDISC_DO 2