diff --git a/src/system/libroot/posix/unistd/alarm.c b/src/system/libroot/posix/unistd/alarm.c
index e47f6e9261..fbfeddcc11 100644
--- a/src/system/libroot/posix/unistd/alarm.c
+++ b/src/system/libroot/posix/unistd/alarm.c
@@ -15,12 +15,17 @@ uint
 alarm(unsigned int sec)
 {
 	struct itimerval value, oldValue;
+	int result;
 
 	value.it_interval.tv_sec = value.it_interval.tv_usec = 0;
 	value.it_value.tv_sec = sec;
 	value.it_value.tv_usec = 0;
-	if (setitimer(ITIMER_REAL, &value, &oldValue) < 0)
+
+	result = setitimer(ITIMER_REAL, &value, &oldValue);
+	if (result < 0) {
+		errno = result;
 		return -1;
+	}
 
 	if (oldValue.it_value.tv_usec)
 		oldValue.it_value.tv_sec++;