diff --git a/weed/s3api/s3api_policy.go b/weed/s3api/s3api_policy.go
index 4177d27f3..6e2c8cfa2 100644
--- a/weed/s3api/s3api_policy.go
+++ b/weed/s3api/s3api_policy.go
@@ -51,7 +51,7 @@ type Prefix struct {
 	set bool
 }
 
-// MarshalXML - decodes XML data.
+// MarshalXML encodes Prefix field into an XML form.
 func (p Prefix) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error {
 	if !p.set {
 		return nil
@@ -59,6 +59,7 @@ func (p Prefix) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error
 	return e.EncodeElement(p.string, startElement)
 }
 
+// MarshalXML encodes Filter field into an XML form.
 func (f Filter) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
 	if err := e.EncodeToken(start); err != nil {
 		return err