diff --git a/cpu/native/periph/timer.c b/cpu/native/periph/timer.c
index 6cf9557683..bd17926f5b 100644
--- a/cpu/native/periph/timer.c
+++ b/cpu/native/periph/timer.c
@@ -66,7 +66,7 @@ static struct itimerval itv;
 static unsigned long ts2ticks(struct timespec *tp)
 {
     /* TODO: check for overflow */
-    return((tp->tv_sec * NATIVE_TIMER_SPEED) + (tp->tv_nsec / 1000));
+    return(((unsigned long)tp->tv_sec * NATIVE_TIMER_SPEED) + (tp->tv_nsec / 1000));
 }
 
 /**