diff --git a/lib/models.py b/lib/models.py
index 7372486..b305a56 100644
--- a/lib/models.py
+++ b/lib/models.py
@@ -91,6 +91,10 @@ class Client(db.Model):
 class Subject(db.Model):
 
   name = db.StringProperty(required=True)
+  readable_only_by = db.ReferenceProperty(
+      reference_class=Profile, collection_name='readable_subject_set')
+  writable_only_by = db.ReferenceProperty(
+      reference_class=Profile, collection_name='writable_subject_set')
 
   @classmethod
   def FindOrCreate(cls, name):
@@ -206,7 +210,9 @@ class Message(db.Model):
       'event_type':   'message',
       'id':           self.key().id(),
       'sender':       str(Message.sender.get_value_for_datastore(self)),
-      'subject':      self.parent().name,
+      'subject':      {
+          'name':         self.parent().name,
+      },
       'created':      self.created,
       'message':      self.message,
     }
diff --git a/static/cosmopolite.js b/static/cosmopolite.js
index b8e8039..b9a722e 100644
--- a/static/cosmopolite.js
+++ b/static/cosmopolite.js
@@ -110,10 +110,15 @@ Cosmopolite.prototype.subscribe = function(subject, messages, keys) {
       'keys': keys,
     };
     this.sendRPC_('subscribe', args, function() {
-      this.subscriptions_[subject] = {
-        'messages': [],
-        'keys': {},
-      };
+      if (subject in this.subscriptions_) {
+        console.log(
+          this.loggingPrefix_(), 'duplicate subject subscriptions:', subject);
+      } else {
+        this.subscriptions_[subject] = {
+          'messages': [],
+          'keys': {},
+        };
+      }
       resolve();
     }.bind(this));
   }.bind(this));
@@ -516,7 +521,7 @@ Cosmopolite.prototype.onServerEvent_ = function(e) {
       }
       break;
     case 'message':
-      var subscription = this.subscriptions_[e['subject']];
+      var subscription = this.subscriptions_[e['subject']['name']];
       if (!subscription) {
         console.log(
           this.loggingPrefix_(),
diff --git a/static/test.js b/static/test.js
index 84e1903..c225423 100644
--- a/static/test.js
+++ b/static/test.js
@@ -94,7 +94,7 @@ asyncTest('Message round trip', function() {
 
   var callbacks = {
     'onMessage': function(e) {
-      equal(e['subject'], subject, 'subject matches');
+      equal(e['subject']['name'], subject, 'subject matches');
       equal(e['message'], message, 'message matches');
       cosmo.shutdown();
       start();
@@ -119,7 +119,7 @@ asyncTest('Overwrite key', function() {
   var callbacks = {
     'onMessage': function(e) {
       messages++;
-      equal(e['subject'], subject, 'subject matches');
+      equal(e['subject']['name'], subject, 'subject matches');
       equal(e['key'], key, 'key matches');
       if (messages == 1) {
         equal(e['message'], message1, 'message #1 matches');
@@ -156,7 +156,7 @@ asyncTest('Complex object', function() {
 
   var callbacks = {
     'onMessage': function(e) {
-      equal(e['subject'], subject, 'subject matches');
+      equal(e['subject']['name'], subject, 'subject matches');
       deepEqual(e['message'], message, 'message matches');
       cosmo.shutdown();
       start();
@@ -209,7 +209,7 @@ asyncTest('Duplicate message suppression', function() {
 
   var callbacks = {
     'onMessage': function (msg) {
-      equal(msg['subject'], subject, 'subject matches');
+      equal(msg['subject']['name'], subject, 'subject matches');
       equal(msg['key'], key, 'key matches');
       equal(msg['message'], message1, 'message matches');
       cosmo.shutdown();
@@ -245,7 +245,7 @@ asyncTest('Message persistence', function() {
 
   var callbacks = {
     'onMessage': function(msg) {
-      equal(msg['subject'], subject, 'subject matches');
+      equal(msg['subject']['name'], subject, 'subject matches');
       equal(msg['message'], message, 'message matches');
       cosmo2.shutdown();
       start();
@@ -297,9 +297,12 @@ asyncTest('Profile merge', function() {
     var callbacks = {
       'onMessage': function(msg) {
         messages++;
-        equal(msg['subject'], subject, 'message #' + messages + ': subject matches');
-        equal(msg['message'], message, 'message #' + messages + ': message matches');
-        equal(msg['sender'], cosmo.profile(), 'message #' + messages + ': profile matches');
+        equal(msg['subject']['name'], subject,
+              'message #' + messages + ': subject matches');
+        equal(msg['message'], message,
+              'message #' + messages + ': message matches');
+        equal(msg['sender'], cosmo.profile(),
+              'message #' + messages + ': profile matches');
         if (messages == 1) {
           cosmo.unsubscribe(subject);
           // Entirely magic URL that sets the login cookie and redirects.