diff --git a/sys/compat/linux/linux_misc.c b/sys/compat/linux/linux_misc.c
index a9c330ac1af..7569644aedd 100644
--- a/sys/compat/linux/linux_misc.c
+++ b/sys/compat/linux/linux_misc.c
@@ -206,6 +206,11 @@ linux_alarm(struct thread *td, struct linux_alarm_args *args)
 	it.it_value.tv_usec = 0;
 	it.it_interval.tv_sec = 0;
 	it.it_interval.tv_usec = 0;
+	/*
+	 * According to POSIX and Linux implementation
+	 * the alarm() system call is always successfull.
+	 * Ignore errors and return 0 as a Linux do.
+	 */
 	kern_setitimer(td, ITIMER_REAL, &it, &old_it);
 	if (timevalisset(&old_it.it_value)) {
 		if (old_it.it_value.tv_usec != 0)