diff --git a/libc/include/sys/timex.h b/libc/include/sys/timex.h
index 4096e7d..6138ac4 100644
--- a/libc/include/sys/timex.h
+++ b/libc/include/sys/timex.h
@@ -29,6 +29,13 @@
 #ifndef _SYS_TIMEX_H_
 #define _SYS_TIMEX_H_
 
+#include <sys/cdefs.h>
 #include <linux/timex.h>
 
+__BEGIN_DECLS
+
+extern int adjtimex(struct timex *buf);
+
+__END_DECLS
+
 #endif /* _SYS_TIMEX_H_ */