diff --git a/libc/include/sys/socketcalls.h b/libc/include/sys/socketcalls.h
index c74f463..09c079f 100644
--- a/libc/include/sys/socketcalls.h
+++ b/libc/include/sys/socketcalls.h
@@ -47,5 +47,6 @@
 #define SYS_GETSOCKOPT  15              /* sys_getsockopt(2)            */
 #define SYS_SENDMSG     16              /* sys_sendmsg(2)               */
 #define SYS_RECVMSG     17              /* sys_recvmsg(2)               */
+#define SYS_ACCEPT4     18              /* sys_accept4(2)               */
 
 #endif /* _SYS_SOCKETCALLS_H_ */