diff --git a/sys/include/libc.h b/sys/include/libc.h
index 4631269..75d0ffd 100644
--- a/sys/include/libc.h
+++ b/sys/include/libc.h
@@ -609,7 +609,7 @@ extern	void*	jehanne_segbrk(uint32_t);
 extern	void*	jehanne_segattach(int, const char*, void*, unsigned long);
 extern	int	jehanne_segdetach(void*);
 extern	int	jehanne_segfree(void*, unsigned long);
-extern	void	jehanne_sleep(int32_t);
+extern	void	jehanne_sleep(unsigned int millisecs);
 extern	int	jehanne_stat(const char*, uint8_t*, int);
 extern	Waitmsg*	jehanne_wait(void);
 extern	int	jehanne_waitpid(void);
diff --git a/sys/src/lib/c/9sys/sleep.c b/sys/src/lib/c/9sys/sleep.c
index 7fe3133..d31d4d2 100644
--- a/sys/src/lib/c/9sys/sleep.c
+++ b/sys/src/lib/c/9sys/sleep.c
@@ -1,7 +1,7 @@
 /*
  * This file is part of Jehanne.
  *
- * Copyright (C) 2015 Giacomo Tesio <giacomo@tesio.it>
+ * Copyright (C) 2015-2017 Giacomo Tesio <giacomo@tesio.it>
  *
  * Jehanne is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,9 +20,9 @@
 #include <libc.h>
 
 void
-jehanne_sleep(int32_t millisecs)
+jehanne_sleep(unsigned int millisecs)
 {
-	int64_t wakeup;
+	long wakeup;
 
 	wakeup = awake(millisecs);	// give up the processor, in any case
 	if(millisecs > 0)