diff --git a/libc/kernel/uapi/linux/in.h b/libc/kernel/uapi/linux/in.h
index 3947d5a..3e98b79 100644
--- a/libc/kernel/uapi/linux/in.h
+++ b/libc/kernel/uapi/linux/in.h
@@ -142,6 +142,7 @@
 #define IP_MULTICAST_ALL 49
 #define IP_UNICAST_IF 50
 #define IP_LOCAL_PORT_RANGE 51
+#define IP_PROTOCOL 52
 #define MCAST_EXCLUDE 0
 #define MCAST_INCLUDE 1
 #define IP_DEFAULT_MULTICAST_TTL 1