diff --git a/fio_time.h b/fio_time.h
index 27520b0..79f324a 100644
--- a/fio_time.h
+++ b/fio_time.h
@@ -10,8 +10,8 @@
 extern uint64_t time_since_genesis(void);
 extern uint64_t mtime_since_genesis(void);
 extern uint64_t utime_since_genesis(void);
-extern void usec_spin(unsigned int);
-extern void usec_sleep(struct thread_data *, unsigned long);
+extern uint64_t usec_spin(unsigned int);
+extern uint64_t usec_sleep(struct thread_data *, unsigned long);
 extern void fill_start_time(struct timeval *);
 extern void set_genesis_time(void);
 extern int ramp_time_over(struct thread_data *);