diff --git a/app/vmstorage/main.go b/app/vmstorage/main.go
index 14eefb5e4..f3be38ff9 100644
--- a/app/vmstorage/main.go
+++ b/app/vmstorage/main.go
@@ -75,7 +75,7 @@ func CheckTimeRange(tr storage.TimeRange) error {
 	if !*denyQueriesOutsideRetention {
 		return nil
 	}
-	minAllowedTimestamp := int64(fasttime.UnixTimestamp()*1000) - retentionPeriod.Duration().Milliseconds()
+	minAllowedTimestamp := int64(fasttime.UnixTimestamp()*1000) - retentionPeriod.Milliseconds()
 	if tr.MinTimestamp > minAllowedTimestamp {
 		return nil
 	}
diff --git a/lib/flagutil/duration.go b/lib/flagutil/duration.go
index 4b565bbaa..e33d1fc13 100644
--- a/lib/flagutil/duration.go
+++ b/lib/flagutil/duration.go
@@ -31,11 +31,16 @@ type Duration struct {
 	valueString string
 }
 
-// Duration convert to time.Duration.
+// Duration returns d as time.Duration
 func (d *Duration) Duration() time.Duration {
 	return time.Millisecond * time.Duration(d.msecs)
 }
 
+// Milliseconds returns d in milliseconds
+func (d *Duration) Milliseconds() int64 {
+	return d.msecs
+}
+
 // String implements flag.Value interface
 func (d *Duration) String() string {
 	return d.valueString
diff --git a/lib/flagutil/duration_test.go b/lib/flagutil/duration_test.go
index bb138605f..f9834c679 100644
--- a/lib/flagutil/duration_test.go
+++ b/lib/flagutil/duration_test.go
@@ -42,8 +42,8 @@ func TestDurationSetSuccess(t *testing.T) {
 		if err := d.Set(value); err != nil {
 			t.Fatalf("unexpected error in d.Set(%q): %s", value, err)
 		}
-		if d.msecs != expectedMsecs {
-			t.Fatalf("unexpected result; got %d; want %d", d.msecs, expectedMsecs)
+		if d.Milliseconds() != expectedMsecs {
+			t.Fatalf("unexpected result; got %d; want %d", d.Milliseconds(), expectedMsecs)
 		}
 		valueString := d.String()
 		valueExpected := strings.ToLower(value)