diff --git a/sys/include/libc.h b/sys/include/libc.h
index 833a3f50b..a16ab4ef4 100644
--- a/sys/include/libc.h
+++ b/sys/include/libc.h
@@ -328,6 +328,8 @@ extern	double	cputime(void);
 extern	long	times(long*);
 extern	long	tm2sec(Tm*);
 extern	vlong	nsec(void);
+extern	char*	isotime(Tm*);
+extern	char*	isodate(Tm*);
 
 extern	void	cycles(uvlong*);	/* 64-bit value of the cycle counter if there is one, 0 if there isn't */