diff --git a/disk/disk_unix.go b/disk/disk_unix.go
index f1f1cf7..9b499b5 100644
--- a/disk/disk_unix.go
+++ b/disk/disk_unix.go
@@ -50,6 +50,8 @@ func UsageWithContext(ctx context.Context, path string) (*UsageStat, error) {
 	if (ret.Used + ret.Free) == 0 {
 		ret.UsedPercent = 0
 	} else {
+		// We don't use ret.Total to calculate percent.
+		// see https://github.com/shirou/gopsutil/issues/562
 		ret.UsedPercent = (float64(ret.Used) / float64(ret.Used+ret.Free)) * 100.0
 	}