diff --git a/bin/sleep/sleep.c b/bin/sleep/sleep.c
--- a/bin/sleep/sleep.c
+++ b/bin/sleep/sleep.c
@@ -59,31 +59,42 @@
 parse_interval(const char *arg)
 {
 	double num;
-	char unit, extra;
-
-	switch (sscanf(arg, "%lf%c%c", &num, &unit, &extra)) {
-	case 2:
-		switch (unit) {
-		case 'd':
-			num *= 24;
-			/* FALLTHROUGH */
-		case 'h':
-			num *= 60;
-			/* FALLTHROUGH */
-		case 'm':
-			num *= 60;
-			/* FALLTHROUGH */
-		case 's':
-			if (!isnan(num))
-				return (num);
-		}
+	char *endptr;
+
+	errno = 0;
+	num = strtod(arg, &endptr);
+
+	/* No number found or overflow */
+	if (endptr == arg || errno != 0 || isnan(num)) {
+		warnx("invalid time interval: %s", arg);
+		return (INFINITY);
+	}
+
+	switch (*endptr) {
+	case '\0':
+	case 's':
+		break;
+	case 'm':
+		num *= 60;
 		break;
-	case 1:
-		if (!isnan(num))
-			return (num);
+	case 'h':
+		num *= 60 * 60;
+		break;
+	case 'd':
+		num *= 24 * 60 * 60;
+		break;
+	default:
+		warnx("invalid time interval: %s", arg);
+		return (INFINITY);
 	}
-	warnx("invalid time interval: %s", arg);
-	return (INFINITY);
+
+	/* Reject trailing garbage like 10ms or 10sx */
+	if (*endptr != '\0' && endptr[1] != '\0') {
+		warnx("invalid time interval: %s", arg);
+		return (INFINITY);
+	}
+
+	return (num);
 }
 
 int
@@ -106,7 +117,7 @@
 	seconds = 0;
 	while (argc--)
 		seconds += parse_interval(*argv++);
-	if (seconds > INT_MAX)
+	if (seconds < 0 || seconds > (double)INT_MAX)
 		usage();
 	if (seconds < 1e-9)
 		exit(0);
@@ -120,8 +131,9 @@
 			err(1, "nanosleep");
 		if (report_requested) {
 			/* Reporting does not bother with nanoseconds. */
-			warnx("about %ld second(s) left out of the original %ld",
+			printf("about %ld second(s) left out of the original %ld\n",
 			    (long)time_to_sleep.tv_sec, (long)original);
+		        fflush(stdout);
 			report_requested = 0;
 		}
 	}