diff --git a/app/vmstorage/main.go b/app/vmstorage/main.go
index e722d6010..4d1ce91b4 100644
--- a/app/vmstorage/main.go
+++ b/app/vmstorage/main.go
@@ -22,7 +22,7 @@ import (
 )
 
 var (
-	retentionPeriod   = flagutil.NewDuration("retentionPeriod", 1, "Data with timestamps outside the retentionPeriod is automatically deleted")
+	retentionPeriod   = flagutil.NewDuration("retentionPeriod", "1", "Data with timestamps outside the retentionPeriod is automatically deleted")
 	snapshotAuthKey   = flag.String("snapshotAuthKey", "", "authKey, which must be passed in query string to /snapshot* pages")
 	forceMergeAuthKey = flag.String("forceMergeAuthKey", "", "authKey, which must be passed in query string to /internal/force_merge pages")
 	forceFlushAuthKey = flag.String("forceFlushAuthKey", "", "authKey, which must be passed in query string to /internal/force_flush pages")
diff --git a/lib/flagutil/duration.go b/lib/flagutil/duration.go
index 8dd920f67..87d602c6e 100644
--- a/lib/flagutil/duration.go
+++ b/lib/flagutil/duration.go
@@ -12,14 +12,14 @@ import (
 // NewDuration returns new `duration` flag with the given name, defaultValue and description.
 //
 // DefaultValue is in months.
-func NewDuration(name string, defaultValue float64, description string) *Duration {
+func NewDuration(name string, defaultValue string, description string) *Duration {
 	description += "\nThe following optional suffixes are supported: h (hour), d (day), w (week), y (year). If suffix isn't set, then the duration is counted in months"
-	d := Duration{
-		Msecs:       int64(defaultValue * msecsPerMonth),
-		valueString: fmt.Sprintf("%g", defaultValue),
+	d := &Duration{}
+	if err := d.Set(defaultValue); err != nil {
+		panic(fmt.Sprintf("BUG: can not parse default value %s for flag %s", defaultValue, name))
 	}
-	flag.Var(&d, name, description)
-	return &d
+	flag.Var(d, name, description)
+	return d
 }
 
 // Duration is a flag for holding duration.
diff --git a/lib/flagutil/duration_test.go b/lib/flagutil/duration_test.go
index 2c35951b3..bd26d47b8 100644
--- a/lib/flagutil/duration_test.go
+++ b/lib/flagutil/duration_test.go
@@ -56,5 +56,6 @@ func TestDurationSetSuccess(t *testing.T) {
 	f("1h", 3600*1000)
 	f("1.5d", 1.5*24*3600*1000)
 	f("2.3W", 2.3*7*24*3600*1000)
+	f("1w", 7*24*3600*1000)
 	f("0.25y", 0.25*365*24*3600*1000)
 }