diff --git a/libc/include/netinet/in_systm.h b/libc/include/netinet/in_systm.h
index 188268e..8da19a5 100644
--- a/libc/include/netinet/in_systm.h
+++ b/libc/include/netinet/in_systm.h
@@ -34,6 +34,7 @@
 #ifndef _NETINET_IN_SYSTM_H_
 #define _NETINET_IN_SYSTM_H_
 
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
 /*