diff --git a/abstract-machine/am/src/platform/nemu/ioe/timer.c b/abstract-machine/am/src/platform/nemu/ioe/timer.c
index 32f5070..4592be6 100644
--- a/abstract-machine/am/src/platform/nemu/ioe/timer.c
+++ b/abstract-machine/am/src/platform/nemu/ioe/timer.c
@@ -3,11 +3,14 @@
 
 #define GET_TIME() ((uint64_t) (uint32_t)inl(RTC_ADDR) | ((uint64_t) (uint32_t)inl(RTC_ADDR + 4) << 32))
 
+uint64_t __timer_start;
+
 void __am_timer_init() {
+  __timer_start = GET_TIME();
 }
 
 void __am_timer_uptime(AM_TIMER_UPTIME_T *uptime) {
-  uptime->us = GET_TIME();
+  (*(volatile AM_TIMER_UPTIME_T *)uptime).us = GET_TIME() - __timer_start;
 }
 
 void __am_timer_rtc(AM_TIMER_RTC_T *rtc) {