diff --git a/src/platforms/posix/px4_layer/drv_hrt.c b/src/platforms/posix/px4_layer/drv_hrt.c
index 0be34240c6..0a45644481 100644
--- a/src/platforms/posix/px4_layer/drv_hrt.c
+++ b/src/platforms/posix/px4_layer/drv_hrt.c
@@ -61,6 +61,7 @@ static void		hrt_call_reschedule(void);
 
 static sem_t 	_hrt_lock;
 static struct work_s	_hrt_work;
+static hrt_abstime px4_timestart = 0;
 
 static void
 hrt_call_invoke(void);
@@ -86,7 +87,6 @@ static void hrt_unlock(void)
 #define clockid_t int
 
 static double px4_timebase = 0.0;
-static uint64_t px4_timestart = 0;
 
 int clock_gettime(clockid_t clk_id, struct timespec *t)
 {
@@ -119,8 +119,13 @@ hrt_abstime hrt_absolute_time(void)
 {
 	struct timespec ts;
 
+	if (!px4_timestart) {
+		clock_gettime(CLOCK_MONOTONIC, &ts);
+		px4_timestart = ts_to_abstime(&ts);
+	}
+
 	clock_gettime(CLOCK_MONOTONIC, &ts);
-	return ts_to_abstime(&ts);
+	return ts_to_abstime(&ts) - px4_timestart;
 }
 
 /*