diff --git a/os_functions.h b/os_functions.h
index 5f6ed6f..347da67 100644
--- a/os_functions.h
+++ b/os_functions.h
@@ -92,9 +92,9 @@ extern int (* OSJoinThread)(void * thread, int * ret_val);
 extern int (* OSSetThreadPriority)(void * thread, int priority);
 extern void (* OSDetachThread)(void * thread);
 extern void (* OSSleepTicks)(u64 ticks);
-extern s64 (* OSGetTick)(void);
-extern s64 (* OSGetTime)(void);
-extern void (*OSTicksToCalendarTime)(s64 time, OSCalendarTime *calendarTime);
+extern u64 (* OSGetTick)(void);
+extern u64 (* OSGetTime)(void);
+extern void (*OSTicksToCalendarTime)(u64 time, OSCalendarTime *calendarTime);
 
 //!----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 //! Mutex functions