diff --git a/activitystreams/activity.go b/activitystreams/activity.go
index cfdab0d..4d42a63 100644
--- a/activitystreams/activity.go
+++ b/activitystreams/activity.go
@@ -1,175 +1,177 @@
 // Package activitystreams provides all the basic ActivityStreams
 // implementation needed for Write.as.
 package activitystreams
 
 import (
 	"time"
 )
 
 const (
 	Namespace = "https://www.w3.org/ns/activitystreams"
 	toPublic  = "https://www.w3.org/ns/activitystreams#Public"
 )
 
 var Extensions = map[string]string{}
 
 // Activity describes actions that have either already occurred, are in the
 // process of occurring, or may occur in the future.
 type Activity struct {
 	BaseObject
-	Actor     string    `json:"actor"`
-	Published time.Time `json:"published,omitempty"`
-	Updated   time.Time `json:"updated,omitempty"`
-	To        []string  `json:"to,omitempty"`
-	CC        []string  `json:"cc,omitempty"`
-	Object    *Object   `json:"object"`
+	Actor     string     `json:"actor"`
+	Published time.Time  `json:"published,omitempty"`
+	Updated   *time.Time `json:"updated,omitempty"`
+	To        []string   `json:"to,omitempty"`
+	CC        []string   `json:"cc,omitempty"`
+	Object    *Object    `json:"object"`
 }
 
 type FollowActivity struct {
 	BaseObject
 	Actor     string    `json:"actor"`
 	Published time.Time `json:"published,omitempty"`
 	To        []string  `json:"to,omitempty"`
 	CC        []string  `json:"cc,omitempty"`
 	Object    string    `json:"object"`
 }
 
 // NewCreateActivity builds a basic Create activity that includes the given
 // Object and the Object's AttributedTo property as the Actor.
 func NewCreateActivity(o *Object) *Activity {
 	a := Activity{
 		BaseObject: BaseObject{
 			Context: []interface{}{
 				Namespace,
 				Extensions,
 			},
 			ID:   o.ID,
 			Type: "Create",
 		},
 		Actor:     o.AttributedTo,
 		Object:    o,
 		Published: o.Published,
 	}
 	return &a
 }
 
 // NewUpdateActivity builds a basic Update activity that includes the given
 // Object and the Object's AttributedTo property as the Actor.
 func NewUpdateActivity(o *Object) *Activity {
 	a := Activity{
 		BaseObject: BaseObject{
 			Context: []interface{}{
 				Namespace,
 				Extensions,
 			},
 			ID:   o.ID,
 			Type: "Update",
 		},
 		Actor:     o.AttributedTo,
 		Object:    o,
 		Published: o.Published,
-		Updated:   o.Updated,
+	}
+	if o.Updated != nil && !o.Updated.IsZero() {
+		a.Updated = o.Updated
 	}
 	return &a
 }
 
 // NewDeleteActivity builds a basic Delete activity that includes the given
 // Object and the Object's AttributedTo property as the Actor.
 func NewDeleteActivity(o *Object) *Activity {
 	a := Activity{
 		BaseObject: BaseObject{
 			Context: []interface{}{
 				Namespace,
 			},
 			ID:   o.ID,
 			Type: "Delete",
 		},
 		Actor:  o.AttributedTo,
 		Object: o,
 	}
 	return &a
 }
 
 // NewFollowActivity builds a basic Follow activity.
 func NewFollowActivity(actorIRI, followeeIRI string) *FollowActivity {
 	a := FollowActivity{
 		BaseObject: BaseObject{
 			Context: []interface{}{
 				Namespace,
 			},
 			Type: "Follow",
 		},
 		Actor:  actorIRI,
 		Object: followeeIRI,
 	}
 	return &a
 }
 
 // Object is the primary base type for the Activity Streams vocabulary.
 type Object struct {
 	BaseObject
 	Published    time.Time         `json:"published,omitempty"`
-	Updated      time.Time         `json:"updated,omitempty"`
+	Updated      *time.Time        `json:"updated,omitempty"`
 	Summary      *string           `json:"summary,omitempty"`
 	InReplyTo    *string           `json:"inReplyTo,omitempty"`
 	URL          string            `json:"url"`
 	AttributedTo string            `json:"attributedTo,omitempty"`
 	To           []string          `json:"to,omitempty"`
 	CC           []string          `json:"cc,omitempty"`
 	Name         string            `json:"name,omitempty"`
 	Content      string            `json:"content,omitempty"`
 	ContentMap   map[string]string `json:"contentMap,omitempty"`
 	Tag          []Tag             `json:"tag,omitempty"`
 	Attachment   []Attachment      `json:"attachment,omitempty"`
 
 	// Person
 	Inbox             string     `json:"inbox,omitempty"`
 	Outbox            string     `json:"outbox,omitempty"`
 	Following         string     `json:"following,omitempty"`
 	Followers         string     `json:"followers,omitempty"`
 	PreferredUsername string     `json:"preferredUsername,omitempty"`
 	Icon              *Image     `json:"icon,omitempty"`
 	PublicKey         *PublicKey `json:"publicKey,omitempty"`
 	Endpoints         *Endpoints `json:"endpoints,omitempty"`
 
 	// Extensions
 	// NOTE: add extensions here
 }
 
 // NewNoteObject creates a basic Note object that includes the public
 // namespace in IRIs it's addressed to.
 func NewNoteObject() *Object {
 	o := Object{
 		BaseObject: BaseObject{
 			Type: "Note",
 		},
 		To: []string{
 			toPublic,
 		},
 	}
 	return &o
 }
 
 // NewArticleObject creates a basic Article object that includes the public
 // namespace in IRIs it's addressed to.
 func NewArticleObject() *Object {
 	o := Object{
 		BaseObject: BaseObject{
 			Type: "Article",
 		},
 		To: []string{
 			toPublic,
 		},
 	}
 	return &o
 }
 
 // NewPersonObject creates a basic Person object.
 func NewPersonObject() *Object {
 	o := Object{
 		BaseObject: BaseObject{
 			Type: "Person",
 		},
 	}
 	return &o
 }